Major error when siege is done

[Vanstredam]

[16:42:15 WARN]: [SiegeWar] Plugin SiegeWar v0.2.1 generated an exception while executing task 111
java.util.ConcurrentModificationException: null
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1493) ~[?:?]
at java.util.HashMap$ValueIterator.next(HashMap.java:1521) ~[?:?]
at com.gmail.goosius.siegewar.tasks.DynmapTask.displaySieges(DynmapTask.java:84) ~[?:?]
at com.gmail.goosius.siegewar.tasks.DynmapTask.lambda$startDynmapTask$0(DynmapTask.java:70) ~[?:?]
at org.bukkit.craftbukkit.v1_16_R3.scheduler.CraftTask.run(CraftTask.java:100) ~[patched_1.16.5.jar:git-Purpur-980]
at org.bukkit.craftbukkit.v1_16_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:58) ~[patched_1.16.5.jar:git-Purpur-980]
at com.destroystokyo.paper.ServerSchedulerReportingWrapper.run(ServerSchedulerReportingWrapper.java:22) ~[patched_1.16.5.jar:git-Purpur-980]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
at java.lang.Thread.run(Thread.java:834) [?:?]

    I don't know the issue for this, it might have to do maybe with the new version?