I’d be willing to buy a 1% resist chance was supposed to exist, we’d just have written that off as lag or something. But there’s no way they had such a huge failure rate in vanilla. I can tell you as a paladin main back then there’s absolutely no way that Cleanse had a 17% miss rate on boss mechanics, and that doesn’t even seem to be happening now which is the clearest sign of a bug.
Seems like they are accidentally using trained spell level rather than caster level and never pushed this change to PTR before it went live.
EDIT: Seems like from more testing it’s literally only Cure Disease that does this at a noticeable rate, so… yay for resurrecting authentic bugs?