I recently switched my server to online mode so that my friends and I from college can play together long-distance. We had an issue where our inventories were lost, but we resolved this by copying playerdata .dat files. Is there a similar way I would be able to change these over?

Background: Offline and Online UUID's for players are different, so the online server sees my account as a new person. My old questing data still exists, but updating QuestingProgress.json with the new UUID in world/betterquesting didn't sync it with my "new" character.

If you're on a recent build, a UUID swap in QuestProgress.json using find-and-replace should have been enough but needs be done while the server is off. NameCache.json may also pose some issues but usually that updates itself (you can just delete it to be sure). I'm starting to wondering if the .dat file you copied contains a conflicting UUID cache.

I don't really know many other things to try besides manually completing what you had with commands. Switching servers between offline and online is generally not recommended for these reasons.

Yeah, I figured that one out the hard way.

Turns out the UUID switch did work, some other settings were just being squirrely, thank you for the help though!