Full error:
java.util.ConcurrentModificationException
at java.base/java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:758)
at java.base/java.util.LinkedHashMap$LinkedValueIterator.next(LinkedHashMap.java:785)
at ru.tehkode.permissions.bukkit.regexperms.PermissiblePEX.permissionValue(PermissiblePEX.java:240)
at ru.tehkode.permissions.bukkit.regexperms.PermissiblePEX.hasPermission(PermissiblePEX.java:127)
at org.bukkit.craftbukkit.v1_16_R3.entity.CraftHumanEntity.hasPermission(CraftHumanEntity.java:214)
at net.minecraft.server.v1_16_R3.CommandDispatcher.lambda$new$0(CommandDispatcher.java:203)
at com.mojang.brigadier.tree.CommandNode.canUse(CommandNode.java:79)
at net.minecraft.server.v1_16_R3.CommandDispatcher.a(CommandDispatcher.java:401)
at net.minecraft.server.v1_16_R3.CommandDispatcher.sendAsync(CommandDispatcher.java:359)
at net.minecraft.server.v1_16_R3.CommandDispatcher.lambda$a$5(CommandDispatcher.java:348)
at java.base/java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1434)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:295)
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1016)
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1665)
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1598)
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)