I've tried them against Nekkers, Endrega, and humans, just to see if one enemy type was somehow resistant, but nope, all 0 damage.
I could've sworn they were effective before, but I don't know what to do with this. I've looked all over the internet for anything related to this bug, but no one's apparently run into this one yet.
I'm on the latest edition of EE, with no mods installed.
EDIT: Figured it out. Apparently, in the latest version at least, if you throw your last bomb, of any type, clearing your inventory of that bomb type, the bomb will have zero effect. Avoidable, but very annoying.