Board Thread:LotR Mod Technical Support/@comment-2A02:1811:B11D:4300:C454:50FA:C140:A22B-20190914131503/@comment-25612015-20190915144950

Then you could use the « --loglevel 1 » or « 2 » switch to analyze your level.dat file (undocumented feature...).

I met a case recently where some standard blocks & items IDs were marked as forbidden. Perhaps there are still blocks & items associated with the original values in your region files, giving a clue as to what these values were originally associated with...

Anyway, --fixunknown should enable you to re-enter your world.