Type of bug

Other unexpected behaviour

/ess dump all output

https://essentialsx.net/dump.html?id=610057a115e9404aac1044b666ce306c

Error log (if applicable)

https://pastebin.com/raw/yz76PZ10

Bug description

Sometimes when a player logs out, a ConcurrentModificationException error occurs

Steps to reproduce

1. Player logs out
2. Error can happen randomly

Expected behaviour

The ConcurrentModificationException does not occur

Actual behaviour

The ConcurrentModificationException can occur

Please do not report bugs unless you are using a supported server setup (CraftBukkit, Spigot, Paper, etc).