Forums: lateinit property not initialized

I can provoke this exception on the log:

15:14:28.221 [AWT-EventQueue-0] WARN  o.b.b.d.RunWithMultipleTemporaryAccounts - Uncaught exception in thread AWT-EventQueue-0
kotlin.UninitializedPropertyAccessException: lateinit property groupItem has not been initialized
	at org.briarproject.briar.desktop.forums.ThreadedConversationViewModel.getGroupItem(ThreadedConversationViewModel.kt:66)
	at org.briarproject.briar.desktop.forums.ThreadedConversationViewModel.eventOccurred(ThreadedConversationViewModel.kt:89)
	at org.briarproject.bramble.event.EventBusImpl.lambda$broadcast$0(EventBusImpl.java:42)
	at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:318)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:773)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:720)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:714)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
	at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

It happens when I run two connected instances and send a message in the forum from one client to the other, while the other one has already opened the forum screen, but not yet opened any specific forum (doesn't need to be the one with the incoming message).