ConcurrentModificationException warnings

[rudde0]

Description

Sometimes skript-gui prints this warning but I don't know what is the cause. Is there any trick to avoid warnings such as this?

Steps to Reproduce

I don't know but I use all features of skript-gui in my scripts (except shape definitions).

Errors / Screenshots

[Server thread/WARN]: [skript-gui] Task #35098396 for skript-gui v1.3 generated an exception
java.util.ConcurrentModificationException: null
    at java.util.WeakHashMap$HashIterator.nextEntry(WeakHashMap.java:815) ~[?:?]
    at java.util.WeakHashMap$ValueIterator.next(WeakHashMap.java:842) ~[?:?]
    at java.util.Collection.removeIf(Collection.java:583) ~[?:?]
    at io.github.apickledwalrus.skriptgui.gui.GUIManager.unregister(GUIManager.java:47) ~[skript-gui-1.3-rudde.jar:?]
    at io.github.apickledwalrus.skriptgui.gui.GUI$1.lambda$onClose$1(GUI.java:102) ~[skript-gui-1.3-rudde.jar:?]
    at org.bukkit.craftbukkit.v1_20_R3.scheduler.CraftTask.run(CraftTask.java:101) ~[purpur-1.20.4.jar:git-Purpur-2137]
    at org.bukkit.craftbukkit.v1_20_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:482) ~[purpur-1.20.4.jar:git-Purpur-2137]
    at net.minecraft.server.MinecraftServer.tickChildren(MinecraftServer.java:1669) ~[purpur-1.20.4.jar:git-Purpur-2137]
    at net.minecraft.server.dedicated.DedicatedServer.tickChildren(DedicatedServer.java:486) ~[purpur-1.20.4.jar:git-Purpur-2137]
    at net.minecraft.server.MinecraftServer.tickServer(MinecraftServer.java:1548) ~[purpur-1.20.4.jar:git-Purpur-2137]
    at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1236) ~[purpur-1.20.4.jar:git-Purpur-2137]
    at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:323) ~[purpur-1.20.4.jar:git-Purpur-2137]
    at java.lang.Thread.run(Thread.java:1583) ~[?:?]

Server Information

• Server version/platform: git-Purpur-2128 (MC: 1.20.4)
• skript-gui version: 1.3
• Skript version: 2.8.1

[Fusezion]

to find the actual cause of this code would likely be needed but this seems related to run on close section possibly.