When running the uitests on Linux, exceptions are seen:

Running org.openjdk.jmc.flightrecorder.uitest.OldRecordingsVerificationTest
Dec 21, 2020 4:09:32 PM org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob run
WARNING: Could not evaluate Threads Allocating
java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
at org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob.run(RuleManager.java:155)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at org.openjdk.jmc.flightrecorder.stacktrace.StacktraceModel$Fork.getBranch(StacktraceModel.java:476)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByThreadRule.getResult(AllocationByThreadRule.java:107)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByThreadRule.access$000(AllocationByThreadRule.java:74)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByThreadRule$1.call(AllocationByThreadRule.java:126)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByThreadRule$1.call(AllocationByThreadRule.java:123)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.lang.Thread.run(Thread.java:834)

(JDK Mission Control:460232): Gtk-WARNING **: 16:09:32.729: Negative content height -1 (allocation 1, extents 1x1) while allocating gadget (node scrolledwindow, owner GtkScrolledWindow)
Dec 21, 2020 4:09:32 PM org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob run
WARNING: Could not evaluate Allocated Classes
java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
at org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob.run(RuleManager.java:155)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at org.openjdk.jmc.flightrecorder.stacktrace.StacktraceModel$Fork.getBranch(StacktraceModel.java:476)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByClassRule.getResult(AllocationByClassRule.java:107)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByClassRule.access$000(AllocationByClassRule.java:74)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByClassRule$1.call(AllocationByClassRule.java:124)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByClassRule$1.call(AllocationByClassRule.java:121)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.lang.Thread.run(Thread.java:834)

(JDK Mission Control:460232): Gtk-CRITICAL **: 16:09:34.404: gtk_box_gadget_distribute: assertion 'size >= 0' failed in GtkScrollbar

(JDK Mission Control:460232): Gtk-WARNING **: 16:09:53.786: Negative content height -1 (allocation 1, extents 1x1) while allocating gadget (node scrolledwindow, owner GtkScrolledWindow)
Dec 21, 2020 4:10:14 PM org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob run
WARNING: Could not evaluate Threads Allocating
java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
at org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob.run(RuleManager.java:155)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at org.openjdk.jmc.flightrecorder.stacktrace.StacktraceModel$Fork.getBranch(StacktraceModel.java:476)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByThreadRule.getResult(AllocationByThreadRule.java:107)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByThreadRule.access$000(AllocationByThreadRule.java:74)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByThreadRule$1.call(AllocationByThreadRule.java:126)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByThreadRule$1.call(AllocationByThreadRule.java:123)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.lang.Thread.run(Thread.java:834)

(JDK Mission Control:460232): Gtk-WARNING **: 16:10:14.776: Negative content height -1 (allocation 1, extents 1x1) while allocating gadget (node scrolledwindow, owner GtkScrolledWindow)
Dec 21, 2020 4:10:14 PM org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob run
WARNING: Could not evaluate Allocated Classes
java.util.concurrent.ExecutionException: java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
at org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob.run(RuleManager.java:155)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
at org.openjdk.jmc.flightrecorder.stacktrace.StacktraceModel$Fork.getBranch(StacktraceModel.java:476)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByClassRule.getResult(AllocationByClassRule.java:107)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByClassRule.access$000(AllocationByClassRule.java:74)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByClassRule$1.call(AllocationByClassRule.java:124)
at org.openjdk.jmc.flightrecorder.rules.jdk.memory.AllocationByClassRule$1.call(AllocationByClassRule.java:121)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.lang.Thread.run(Thread.java:834)

(JDK Mission Control:460232): Gtk-CRITICAL **: 16:10:16.438: gtk_box_gadget_distribute: assertion 'size >= 0' failed in GtkScrollbar

(JDK Mission Control:460232): Gtk-WARNING **: 16:10:35.701: Negative content height -1 (allocation 1, extents 1x1) while allocating gadget (node scrolledwindow, owner GtkScrolledWindow)

(JDK Mission Control:460232): Gtk-CRITICAL **: 16:10:37.308: gtk_box_gadget_distribute: assertion 'size >= 0' failed in GtkScrollbar

(JDK Mission Control:460232): Gtk-WARNING **: 16:10:57.196: Negative content height -1 (allocation 1, extents 1x1) while allocating gadget (node scrolledwindow, owner GtkScrolledWindow)

(JDK Mission Control:460232): Gtk-CRITICAL **: 16:10:58.806: gtk_box_gadget_distribute: assertion 'size >= 0' failed in GtkScrollbar

(JDK Mission Control:460232): Gtk-WARNING **: 16:11:18.423: Negative content height -1 (allocation 1, extents 1x1) while allocating gadget (node scrolledwindow, owner GtkScrolledWindow)

(JDK Mission Control:460232): Gtk-CRITICAL **: 16:11:20.023: gtk_box_gadget_distribute: assertion 'size >= 0' failed in GtkScrollbar

(JDK Mission Control:460232): Gtk-WARNING **: 16:11:39.590: Negative content height -1 (allocation 1, extents 1x1) while allocating gadget (node scrolledwindow, owner GtkScrolledWindow)
Tests run: 7, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 148.358 s - in org.openjdk.jmc.flightrecorder.uitest.OldRecordingsVerificationTest
verifyRecording[Recording file 7u40.jfr](org.openjdk.jmc.flightrecorder.uitest.OldRecordingsVerificationTest) Time elapsed: 20.875 s
verifyRecording[Recording file 7u60.jfr](org.openjdk.jmc.flightrecorder.uitest.OldRecordingsVerificationTest) Time elapsed: 21.068 s
verifyRecording[Recording file 7u76.jfr](org.openjdk.jmc.flightrecorder.uitest.OldRecordingsVerificationTest) Time elapsed: 21.034 s
verifyRecording[Recording file 8u0.jfr](org.openjdk.jmc.flightrecorder.uitest.OldRecordingsVerificationTest) Time elapsed: 21.043 s
verifyRecording[Recording file 8u20.jfr](org.openjdk.jmc.flightrecorder.uitest.OldRecordingsVerificationTest) Time elapsed: 21.487 s
verifyRecording[Recording file 8u40.jfr](org.openjdk.jmc.flightrecorder.uitest.OldRecordingsVerificationTest) Time elapsed: 21.333 s
verifyRecording[Recording file 8u60.jfr](org.openjdk.jmc.flightrecorder.uitest.OldRecordingsVerificationTest) Time elapsed: 21.204 s

As well intermittently, there are NPE's in the logs:

!MESSAGE An internal error occurred during: "ManagementAgent".
!STACK 0
java.lang.NullPointerException
at org.openjdk.jmc.flightrecorder.ui.overview.ResultReportUi.updateRule(ResultReportUi.java:375)
at org.openjdk.jmc.flightrecorder.ui.overview.ResultOverview.updateRule(ResultOverview.java:255)
at org.openjdk.jmc.flightrecorder.ui.overview.ResultOverview.lambda$0(ResultOverview.java:238)
at org.openjdk.jmc.flightrecorder.ui.RuleManager.lambda$3(RuleManager.java:245)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
at java.base/java.util.Collections$SynchronizedCollection.forEach(Collections.java:2067)
at org.openjdk.jmc.flightrecorder.ui.RuleManager.updateListeners(RuleManager.java:245)
at org.openjdk.jmc.flightrecorder.ui.RuleManager.access$4(RuleManager.java:240)
at org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob.run(RuleManager.java:182)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
!SUBENTRY 1 org.eclipse.core.jobs 4 2 2020-12-18 12:08:30.115
!MESSAGE An internal error occurred during: "Allocations.thread".
!STACK 0
java.lang.NullPointerException
at org.openjdk.jmc.flightrecorder.ui.overview.ResultReportUi.updateRule(ResultReportUi.java:375)
at org.openjdk.jmc.flightrecorder.ui.overview.ResultOverview.updateRule(ResultOverview.java:255)
at org.openjdk.jmc.flightrecorder.ui.overview.ResultOverview.lambda$0(ResultOverview.java:238)
at org.openjdk.jmc.flightrecorder.ui.RuleManager.lambda$3(RuleManager.java:245)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
at java.base/java.util.Collections$SynchronizedCollection.forEach(Collections.java:2067)
at org.openjdk.jmc.flightrecorder.ui.RuleManager.updateListeners(RuleManager.java:245)
at org.openjdk.jmc.flightrecorder.ui.RuleManager.access$4(RuleManager.java:240)
at org.openjdk.jmc.flightrecorder.ui.RuleManager$EvaluateJob.run(RuleManager.java:182)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)