appcds/customLoader/HelloCustom_JFR.java failed due to "should have been unloaded"

The following test failed in the JDK15 CI:

runtime/cds/appcds/customLoader/HelloCustom_JFR.java

Here's a snippet from the log file:

Command line: [/scratch/mesos/jib-master/install/jdk-15+15-591/macosx-x64-debug.jdk/jdk-15/fastdebug/bin/java -cp /scratch/mesos/slaves/b0d836b1-c68c-4dbd-8b78-5085890ddd4c-S924/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/0c107d64-3ef6-4ef2-bd92-6d7187ebd80f/runs/e3a288f4-55a1-4b84-a7a7-2e8bbc039b10/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/classes/3/runtime/cds/appcds/customLoader/HelloCustom_JFR.d:/scratch/mesos/jib-master/install/jdk-15+15-591/src.full/open/test/hotspot/jtreg/runtime/cds/appcds/customLoader:/scratch/mesos/slaves/b0d836b1-c68c-4dbd-8b78-5085890ddd4c-S924/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/0c107d64-3ef6-4ef2-bd92-6d7187ebd80f/runs/e3a288f4-55a1-4b84-a7a7-2e8bbc039b10/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/classes/3/test/lib:/scratch/mesos/slaves/b0d836b1-c68c-4dbd-8b78-5085890ddd4c-S924/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/0c107d64-3ef6-4ef2-bd92-6d7187ebd80f/runs/e3a288f4-55a1-4b84-a7a7-2e8bbc039b10/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/classes/3/test/hotspot/jtreg/runtime/cds/appcds:/scratch/mesos/slaves/b0d836b1-c68c-4dbd-8b78-5085890ddd4c-S924/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/0c107d64-3ef6-4ef2-bd92-6d7187ebd80f/runs/e3a288f4-55a1-4b84-a7a7-2e8bbc039b10/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/classes/3/runtime/testlibrary:/scratch/mesos/jib-master/install/jtreg/5.0/b01/bundles/jtreg_bin-5.0.zip/jtreg/lib/javatest.jar:/scratch/mesos/jib-master/install/jtreg/5.0/b01/bundles/jtreg_bin-5.0.zip/jtreg/lib/jtreg.jar -XX:MaxRAMPercentage=5 -XX:+CreateCoredumpOnCrash -XX:+UnlockExperimentalVMOptions -XX:+UseZGC -Xshare:on -showversion -XX:SharedArchiveFile=/scratch/mesos/slaves/b0d836b1-c68c-4dbd-8b78-5085890ddd4c-S924/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/0c107d64-3ef6-4ef2-bd92-6d7187ebd80f/runs/e3a288f4-55a1-4b84-a7a7-2e8bbc039b10/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/scratch/0/appcds-11h26m07s399.jsa -Dtest.timeout.factor=10.0 -cp /scratch/mesos/slaves/b0d836b1-c68c-4dbd-8b78-5085890ddd4c-S924/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/0c107d64-3ef6-4ef2-bd92-6d7187ebd80f/runs/e3a288f4-55a1-4b84-a7a7-2e8bbc039b10/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/scratch/0/hello.jar -XX:StartFlightRecording=dumponexit=true -Xlog:cds+jvmti=debug -Xbootclasspath/a:/scratch/mesos/slaves/b0d836b1-c68c-4dbd-8b78-5085890ddd4c-S924/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/0c107d64-3ef6-4ef2-bd92-6d7187ebd80f/runs/e3a288f4-55a1-4b84-a7a7-2e8bbc039b10/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/scratch/0/WhiteBox.jar -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI HelloUnload /scratch/mesos/slaves/b0d836b1-c68c-4dbd-8b78-5085890ddd4c-S924/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/0c107d64-3ef6-4ef2-bd92-6d7187ebd80f/runs/e3a288f4-55a1-4b84-a7a7-2e8bbc039b10/testoutput/test-support/jtreg_open_test_hotspot_jtreg_hotspot_runtime/scratch/0/hello_custom.jar true true ]
[2020-03-16T11:26:09.925235Z] Gathering output for process 73534
[ELAPSED: 4588 ms]
[logging stdout to HelloCustom_JFR-0001-exec.stdout]
[logging stderr to HelloCustom_JFR-0001-exec.stderr]
[STDERR]
java version "15-ea" 2020-09-15
Java(TM) SE Runtime Environment (fastdebug build 15-ea+15-591)
Java HotSpot(TM) 64-Bit Server VM (fastdebug build 15-ea+15-591, mixed mode, sharing)
Exception in thread "main" ClassUnloadCommon$TestFailure: Test failed: should have been unloaded
at ClassUnloadCommon.failIf(ClassUnloadCommon.java:50)
at HelloUnload.main(HelloUnload.java:95)

[2020-03-16T11:26:14.510808Z] Waiting for completion for process 73534
[2020-03-16T11:26:14.511159Z] Waiting for completion finished for process 73534
[2020-03-16T11:26:14.511290Z] Waiting for completion for process 73534
[2020-03-16T11:26:14.511365Z] Waiting for completion finished for process 73534
[2020-03-16T11:26:14.532381Z] Waiting for completion for process 73534
[2020-03-16T11:26:14.532535Z] Waiting for completion finished for process 73534
----------System.err:(170/28864)----------