Certain items don't have the corresponding Language data.

It was in a Dungeon Crawl Dungeon.

Was your world previously on 1.18?

This is my 1.19 test bench for my mod upgrade, i did copy some things over.

There is no affix with id apotheosis:stalwart in 1.19.
How did you obtain this item?

Affix nbt is locked in at generation time, so old data becomes stale when renames happen. This isn't really a bug, and there's no way to migrate them, just that there was a breaking rename in the 18->19 change.

You won't see this on new items, so this is safe to close