Reposting this issue since it seems it's a Steve's Carts issue.

The following issue appears when joining a server around the new year:

There are 1 missing entries in this save.
If you continue the missing entries will get removed.
A world backup will be automatically created in your saves directory.

Missing minecraft:villagerprofessions:
    stevescarts:santa


Run the command /fml confirm or or /fml cancel to proceed.
Alternatively start the server with -Dfml.queryResult=confirm or -Dfml.queryResult=cancel to preselect the answer.

Users are able to pass -Dfml.queryResult=confirm with mixed success. Ideally, since this flag confirms for all prompts across all mods, the solution would be to fix this mod-side so users can omit passing this.

More specific info in parent thread.

For the record we were unable to recover our world using this method and are attempting to recover from a backup.

This issue was fixed years ago. Sadly I wasn’t aware that this was contained in the mod so it should never of happened. (I only helped port it).

I see no reason why the worlds shouldn’t work after allowing the removed entries.