Everything seems to be working fine with the 1.20.2 version of MapFrontiers with what I have tested, but after saving a world in 1.20.4 and opening the world back up it crashes.
I hope this log can help.
crash-2023-12-27_06.39.29-server.txt

The version for 1.20.2 does not work on 1.20.4.
I'm working on that version.