1 critical, 2 warnings found. Every finding below comes from what was actually in the pasted files. Treat the fixes as suggestions: they cover the common causes, and this case may need more digging.
Paper 1.21.11-132-ver/1.21.11@c5eb079Minecraft 1.21.11
What this error means, and every way to fix it →
The server ran out of metaspace, not heap
Class metadata space filled up, which happens with very large modpacks or a -XX:MaxMetaspaceSize cap set too low. Remove any MaxMetaspaceSize flag from the start command, or raise it. More -Xmx does not help this one.
jump to line 463This server is issuing offline-mode identities (Milan_Playexx got a name-derived UUID)
The UUIDs handed out at login are version 3, generated from the username instead of issued by Mojang (Milan_Playexx was given f5855943-6981-39da-bbad-a228a957f88d). That means online-mode=false, or a proxy in front that is not forwarding real identities. Two consequences, both worse than they look. Anyone can join under any name, including your admins, because nothing checks the account. And the UUID is the player identity: flip online-mode back to true and every inventory, home, claim and permission tied to the old UUID looks lost, because the player is now a different person to the server. Set online-mode=true in server.properties before the world has history, or configure proper forwarding if a proxy is meant to be handling authentication.
jump to line 457ProtocolLib does not match this Minecraft version
ProtocolLib, or a plugin built on it, predates the Minecraft version you run. Its internals reach into server code that moved. Install the latest ProtocolLib build for your exact Minecraft version (dev builds after an update). If errors continue, the plugin using it needs updating too.
jump to line 61As received, after redaction.
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