Board Thread:LotR Mod Technical Support/@comment-2A02:1811:B11D:4300:C454:50FA:C140:A22B-20190914131503/@comment-25612015-20190914225827

You probably installed and then removed some mod which added a handful of blocks and some items, which were used somewhere in your region files.

Use the -u / —-unknown switch to fix this, though it will leave holes in your region files as there million of uses of these blocks.

Alternatively, you could safely delete any missing item ID’ and replace missing blocks by AMBIANT blocks.

Make a save of your region files to try both approaches...