Open the hotmethods_before.jfr file from the tutorial. Make the flame view visible. Click on the Java Application page:

Exception in thread "GraphModelCalculation-2" java.lang.ClassCastException: class java.lang.String cannot be cast to class org.openjdk.jmc.common.IMCStackTrace (java.lang.String is in module java.base of loader 'bootstrap'; org.openjdk.jmc.common.IMCStackTrace is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @3d19d85)
Exception in thread "FlameGraphModelCalculation-2" at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.getStackTrace(StacktraceGraphModel.java:354)
at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.addItem(StacktraceGraphModel.java:279)
at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.lambda$buildModel$1(StacktraceGraphModel.java:266)
at java.base/java.lang.Iterable.forEach(Iterable.java:75)
at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.buildModel(StacktraceGraphModel.java:266)
at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.<init>(StacktraceGraphModel.java:116)
at org.openjdk.jmc.flightrecorder.graphview.views.GraphView$ModelRebuildRunnable.run(GraphView.java:120)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
at java.base/java.lang.Thread.run(Thread.java:832)
java.lang.ClassCastException: class java.lang.String cannot be cast to class org.openjdk.jmc.common.IMCStackTrace (java.lang.String is in module java.base of loader 'bootstrap'; org.openjdk.jmc.common.IMCStackTrace is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @3d19d85)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.getStackTrace(StacktraceTreeModel.java:221)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.addItem(StacktraceTreeModel.java:164)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.lambda$new$0(StacktraceTreeModel.java:145)
at java.base/java.lang.Iterable.forEach(Iterable.java:75)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.<init>(StacktraceTreeModel.java:145)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.<init>(StacktraceTreeModel.java:117)
at org.openjdk.jmc.flightrecorder.flameview.views.FlameGraphView$ModelRebuildRunnable.run(FlameGraphView.java:307)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
at java.base/java.lang.Thread.run(Thread.java:832)
Exception in thread "FlameGraphModelCalculation-1" java.lang.ClassCastException: class org.openjdk.jmc.flightrecorder.internal.parser.v1.StructTypes$JfrThread cannot be cast to class org.openjdk.jmc.common.IMCStackTrace (org.openjdk.jmc.flightrecorder.internal.parser.v1.StructTypes$JfrThread is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @493968a9; org.openjdk.jmc.common.IMCStackTrace is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @3d19d85)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.getStackTrace(StacktraceTreeModel.java:221)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.addItem(StacktraceTreeModel.java:164)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.lambda$new$0(StacktraceTreeModel.java:145)
at java.base/java.lang.Iterable.forEach(Iterable.java:75)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.<init>(StacktraceTreeModel.java:145)
Exception in thread "GraphModelCalculation-0" at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.<init>(StacktraceTreeModel.java:117)
at org.openjdk.jmc.flightrecorder.flameview.views.FlameGraphView$ModelRebuildRunnable.run(FlameGraphView.java:307)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
at java.base/java.lang.Thread.run(Thread.java:832)
java.lang.ClassCastException: class java.lang.String cannot be cast to class org.openjdk.jmc.common.IMCStackTrace (java.lang.String is in module java.base of loader 'bootstrap'; org.openjdk.jmc.common.IMCStackTrace is in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @3d19d85)
at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.getStackTrace(StacktraceGraphModel.java:354)
at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.addItem(StacktraceGraphModel.java:279)
at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.lambda$buildModel$1(StacktraceGraphModel.java:266)
at java.base/java.lang.Iterable.forEach(Iterable.java:75)
at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.buildModel(StacktraceGraphModel.java:266)
at org.openjdk.jmc.flightrecorder.stacktrace.graph.StacktraceGraphModel.<init>(StacktraceGraphModel.java:116)
at org.openjdk.jmc.flightrecorder.graphview.views.GraphView$ModelRebuildRunnable.run(GraphView.java:120)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
at java.base/java.lang.Thread.run(Thread.java:832)
Exception in thread "GraphModelCalculation-1" java.lang.ClassCastException
Exception in thread "FlameGraphModelCalculation-3" java.lang.ClassCastException: class org.openjdk.jmc.common.unit.ScalarQuantity$DoubleStored cannot be cast to class org.openjdk.jmc.common.IMCStackTrace (org.openjdk.jmc.common.unit.ScalarQuantity$DoubleStored and org.openjdk.jmc.common.IMCStackTrace are in unnamed module of loader org.eclipse.osgi.internal.loader.EquinoxClassLoader @3d19d85)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.getStackTrace(StacktraceTreeModel.java:221)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.addItem(StacktraceTreeModel.java:164)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.lambda$new$0(StacktraceTreeModel.java:145)
at java.base/java.lang.Iterable.forEach(Iterable.java:75)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.<init>(StacktraceTreeModel.java:145)
at org.openjdk.jmc.flightrecorder.stacktrace.tree.StacktraceTreeModel.<init>(StacktraceTreeModel.java:117)
at org.openjdk.jmc.flightrecorder.flameview.views.FlameGraphView$ModelRebuildRunnable.run(FlameGraphView.java:307)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
at java.base/java.lang.Thread.run(Thread.java:832)