I keep experiencing this error while I'm playing (luckily VanillaFix prevents it from interrupting the game). It seems to occur when I get an achievement that does not have a Title attached to it (I think only for achievements added by mods).

https://pastebin.com/T6m8QBYf

It was caused by a mod not sticking to the traditional advancement .lang key pattern (i.e. advancement.<mod_id>.<advancement_name>). Can you identify the mod that caused this (most likely the one with the advancement you tried to get as it error'ed), so I can test my fix and make sure it works?

I checked my logs and it looks to be Electroblob's Wizardry.