I get this error in the console from time to time, no specifc pattern: https://pastebin.com/Hi1DqXcU

config.yml: https://pastebin.com/cxVkw86H
items.yml: https://pastebin.com/7HjBuGEU

• ItemJoin v5.2.1-RELEASE-b678
• Purpur 1.16.5

I would suggest updating as this error seems familiar so I am willing to bet it is already fixed.
v5.2.2 is that latest release but I suggest the v5.2.3 snapshot as it is more stable.

Link; https://ci.craftationgaming.com/job/ItemJoin/750/
Remember to remove your old ItemJoin.jar file

Let me know!~

Thanks, should be fixed. I'll take your word for it since I can't access to the server rn.