Server was running perfectly fine until last night when the server crashed randomly. Tried loading it back up but kept getting this error, we're playing the benchmark II modpack and I was told to report this issue by chuunkyz who is an admin in the benchmark II discord. Thank you <3
crash-2022-03-24_01.27.04-server.txt

Sorry, it seems I never saw this.
There's not enough information here, can you send the log files, if you still have them?
Also, has this issue occurred again since then?

I don't think this is something that can be easily reproduced.
It seems like the Waystone save file might be getting corrupted somehow. Maybe with the server trying to save the end and update the waystone data simultaneously?
I can make a "fix" where the error is ignored and it doesn't produce a crash, but in case the data fails to load, it would override it.
Maybe I can figure out something better if I had the world file as well as the fw_waystones.dat Waystones save file.

latest (1).log
crash-2022-12-11_19.40.59-server.txt
Ran into this same issue; the server was working perfectly fine, but this morning it stopped working with the same error. Is there a fix yet? Attached is the log file and crash report.
EDIT: I was just informed that one of my friends placed a Waystone in the End Dimension last night before the issue started occurring. Hope this helps.