Mod version: 6.1.5
About #818, I found Apotheosis boss dropped item always includes misc.apotheosis.affix_name.three suffix, and this item cannot be renamed by anvil. Even changing the language to English, this bug doesn't be fixed.

This issue was present in 6.1.4, but does not persist in 6.1.5 - However, the fix is not retroactive. Reforging the item can fix the name though.