ADDITIONAL SYSTEM INFORMATION :
In this case, windows 11, java "16.0.1", but this is not new. AFAIK it has been a problem
since the beginning of time.

A DESCRIPTION OF THE PROBLEM :
JPopupMenu occasionally gets errors at many phases of their life cycle. I believe
these are all threading errors, caused by asynchronous events in multiple threads.
Some are synchronous with the "show" function, others are not. Some are in paths
where it is possible to catch errors, others are not. Here are a sampling of stack traces:

Thread [AWT-EventQueue-0] (Suspended (exception ArrayIndexOutOfBoundsException))
MenuSelectionManager.getSelectedPath() line: 150
BasicMenuUI$Handler.mousePressed(MouseEvent) line: 524
IconMenu(Component).processMouseEvent(MouseEvent) line: 6614
IconMenu(JComponent).processMouseEvent(MouseEvent) line: 3342
IconMenu(JMenu).processMouseEvent(MouseEvent) line: 82
IconMenu(Component).processEvent(AWTEvent) line: 6382
IconMenu(Container).processEvent(AWTEvent) line: 2264
IconMenu(Component).dispatchEventImpl(AWTEvent) line: 4993
IconMenu(Container).dispatchEventImpl(AWTEvent) line: 2322
IconMenu(Component).dispatchEvent(AWTEvent) line: 4825
LightweightDispatcher.retargetMouseEvent(Component, int, MouseEvent) line: 4934
LightweightDispatcher.processMouseEvent(MouseEvent) line: 4560
LightweightDispatcher.dispatchEvent(AWTEvent) line: 4504
XFrame(Container).dispatchEventImpl(AWTEvent) line: 2308
XFrame(Window).dispatchEventImpl(AWTEvent) line: 2773
XFrame(Component).dispatchEvent(AWTEvent) line: 4825
EventQueue.dispatchEventImpl(AWTEvent, Object) line: 772
EventQueue$4.run() line: 721
EventQueue$4.run() line: 715
AccessController.executePrivileged(PrivilegedAction<T>, AccessControlContext, Class<?>) line: 753
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: 391
ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext, AccessControlContext) line: 85
ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext) line: 95
EventQueue$5.run() line: 745
EventQueue$5.run() line: 743
AccessController.executePrivileged(PrivilegedAction<T>, AccessControlContext, Class<?>) line: 753
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: 391
ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext, AccessControlContext) line: 85
EventQueue.dispatchEvent(AWTEvent) line: 742
EventDispatchThread.pumpOneEventForFilters(int) line: 203
EventDispatchThread.pumpEventsForFilter(int, Conditional, EventFilter) line: 124
EventDispatchThread.pumpEventsForHierarchy(int, Conditional, Component) line: 113
EventDispatchThread.pumpEvents(int, Conditional) line: 109
EventDispatchThread.pumpEvents(Conditional) line: 101
EventDispatchThread.run() line: 90

Thread [Game ] (Suspended (exception ArrayIndexOutOfBoundsException))
owns: Vector<E> (id=95)
Vector<E>.elementAt(int) line: 466
MenuSelectionManager.setSelectedPath(MenuElement[]) line: 126
JPopupMenu(JPopupMenu).setVisible(boolean) line: 777
JPopupMenu(JPopupMenu).show(Component, int, int) line: 957
JPopupMenu.show(Component, int, int) line: 33
G.show(Component, MenuInterface, int, int) line: 2036
XFrame.show(MenuInterface, int, int) line: 293
RepaintManager.showMenu(MenuInterface, MenuParentInterface, int, int) line: 295
HiveGameViewer(exCanvas).show(MenuInterface, int, int) line: 2264
PopupManager$bsSwingMenu.show(MenuParentInterface, int, int) line: 95
PopupManager.show(int, int) line: 282
HiveGameViewer(commonCanvas).doRestorePanZoom(int, int) line: 5124
HiveGameViewer(commonCanvas).handleDeferredEvent(Object, String) line: 5026
HiveGameViewer.handleDeferredEvent(Object, String) line: 95
DeferredEventManager.handleDeferredEvent(DeferredEventHandler) line: 87
HiveGameViewer(exCanvas).ViewerRun(int) line: 1763
HiveGameViewer(commonCanvas).ViewerRun(int) line: 6687
Game(commonPanel).runStep(int) line: 334
Game.runStep(int) line: 3872
Game.run() line: 3918
Thread.run() line: 831

Thread [AWT-EventQueue-0] (Suspended (exception ArrayIndexOutOfBoundsException))
owns: Vector<E> (id=95)
Vector<E>.elementAt(int) line: 466
MenuSelectionManager.setSelectedPath(MenuElement[]) line: 119
BasicMenuUI.appendPath(MenuElement[], MenuElement) line: 264
BasicMenuUI$Handler.mousePressed(MouseEvent) line: 530
IconMenu(Component).processMouseEvent(MouseEvent) line: 6614
IconMenu(JComponent).processMouseEvent(MouseEvent) line: 3342
IconMenu(JMenu).processMouseEvent(MouseEvent) line: 82
IconMenu(Component).processEvent(AWTEvent) line: 6382
IconMenu(Container).processEvent(AWTEvent) line: 2264
IconMenu(Component).dispatchEventImpl(AWTEvent) line: 4993
IconMenu(Container).dispatchEventImpl(AWTEvent) line: 2322
IconMenu(Component).dispatchEvent(AWTEvent) line: 4825
LightweightDispatcher.retargetMouseEvent(Component, int, MouseEvent) line: 4934
LightweightDispatcher.processMouseEvent(MouseEvent) line: 4560
LightweightDispatcher.dispatchEvent(AWTEvent) line: 4504
XFrame(Container).dispatchEventImpl(AWTEvent) line: 2308
XFrame(Window).dispatchEventImpl(AWTEvent) line: 2773
XFrame(Component).dispatchEvent(AWTEvent) line: 4825
EventQueue.dispatchEventImpl(AWTEvent, Object) line: 772
EventQueue$4.run() line: 721
EventQueue$4.run() line: 715
AccessController.executePrivileged(PrivilegedAction<T>, AccessControlContext, Class<?>) line: 753
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: 391
ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext, AccessControlContext) line: 85
ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext) line: 95
EventQueue$5.run() line: 745
EventQueue$5.run() line: 743
AccessController.executePrivileged(PrivilegedAction<T>, AccessControlContext, Class<?>) line: 753
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: 391
ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext, AccessControlContext) line: 85
EventQueue.dispatchEvent(AWTEvent) line: 742
EventDispatchThread.pumpOneEventForFilters(int) line: 203
EventDispatchThread.pumpEventsForFilter(int, Conditional, EventFilter) line: 124
EventDispatchThread.pumpEventsForHierarchy(int, Conditional, Component) line: 113
EventDispatchThread.pumpEvents(int, Conditional) line: 109
EventDispatchThread.pumpEvents(Conditional) line: 101
EventDispatchThread.run() line: 90

java version "16.0.1" 2021-04-20
Java(TM) SE Runtime Environment (build 16.0.1+9-24)
Java HotSpot(TM) 64-Bit Server VM (build 16.0.1+9-24, mixed mode, sharing)

G:\share\projects\boardspace-html\htdocs\java\v102>java -jar OnlineLobby.jar
Screen 20.0 x 11.25 = 22.946949688357275
Udp service server=false
Switch to https://Boardspace.net/hive/hivegames/
Show failed for bridge.JPopupMenu[,0,0,0x0,invalid,layout=javax.swing.plaf.basic.DefaultMenuLayout,alignmentX=0.0,alignmentY=0.0,border=javax.swing.plaf.metal.MetalBorders$PopupMenuBorder@7d85a9d6,flags=8,maximumSize=,minimumSize=,preferredSize=,desiredLocationX=696,desiredLocationY=178,label=,lightWeightPopupEnabled=false,margin=,paintBorder=true] java.lang.ArrayIndexOutOfBoundsException: 0 >= 0




STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
any simple swing menu that is created and shown at runtime. just pound on the
life cycle - show, select. It takes a hundred clicks or so.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Menus ought to be reliable.

ACTUAL -
They're not.

CUSTOMER SUBMITTED WORKAROUND :
Partial workaround is to catch errors where possible and retry.



FREQUENCY : occasionally