CLIENT - unhandled error in GUI - ConcurrentModificationException

Error type: CLIENT - unhandled error in GUI - ConcurrentModificationException

Client version: 1.4.60-V1 (build: 2026-06-20 17:21)
Java version: 1.8.0_471
Default charset: UTF-8

ConcurrentModificationException - look at server or client logs for more details

Stack trace:
java.util.ArrayList$ArrayListSpliterator.forEachRemaining(Unknown Source)
java.util.stream.AbstractPipeline.copyInto(Unknown Source)
java.util.stream.ForEachOps$ForEachTask.compute(Unknown Source)
java.util.concurrent.CountedCompleter.exec(Unknown Source)
java.util.concurrent.ForkJoinTask.doExec(Unknown Source)
java.util.concurrent.ForkJoinPool.helpComplete(Unknown Source)
java.util.concurrent.ForkJoinPool.externalHelpComplete(Unknown Source)
java.util.concurrent.ForkJoinTask.externalAwaitDone(Unknown Source)
java.util.concurrent.ForkJoinTask.doInvoke(Unknown Source)
java.util.concurrent.ForkJoinTask.invoke(Unknown Source)
and other 9 lines

Start by reproducing the GUI error with the reported client version and inspect the server and client logs for the omitted stack-trace lines. Trace the ConcurrentModificationException from the ArrayList stream operation to its application-level caller; done means the triggering path is identified and the error no longer occurs under the same conditions.

Written by the indexing model from the issue text.