**Problem**: Presumably https://git.fortiss.org/af3/af3/-/issues/4240 introduced the following crash in the `MarkerService`. `!STACK 0 java.util.ConcurrentModificationException at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1043) at java.base/java.util.ArrayList$Itr.next(ArrayList.java:997) at org.fortiss.tooling.kernel.ui.internal.MarkerService$CacheEntry$1.runInUIThread(MarkerService.java:268) at org.eclipse.ui.progress.UIJob.lambda$0(UIJob.java:95) at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:40) at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:185) at org.eclipse.swt.widgets.Display.runAsyncMessages(Display.java:3963) at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3590) at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$5.run(PartRenderingEngine.java:1160) at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338) at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1049) at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:155) at org.eclipse.ui.internal.Workbench.lambda$3(Workbench.java:660) at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:338) at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:559) at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:154) at org.fortiss.af3.rcp.application.AF3Application.start(AF3Application.java:49) at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:203) at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:137) at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:107) at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:401) at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:255) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:566) at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:657) at org.eclipse.equinox.launcher.Main.basicRun(Main.java:594) at org.eclipse.equinox.launcher.Main.run(Main.java:1465) at org.eclipse.equinox.launcher.Main.main(Main.java:1438)` **Steps-to-repeat**: - Not 100% reproducible since the concurrent modification exception within the MarkerService depends on the timing behavior (e.g., order in which plugins are started, time that is required for the constraint checks, ...) - The stack trace was collected when starting AutoFOCUS in a workspace with a number of models. **Suggested fix**: Create copies of lists before iterating over them.