It's something fucked up on their end, lots of users are affected (also since long before this dislike count thing happened), and they're in no hurry to fix it.
And there's no point posting on support.google.com about it because clueless "Product Experts", aka non-employees who don't actually know anything, will just parrot the same old "Oh your comment must've been detected as spam" "Oh your comment must've violated Youtube policies" "Oh the channel owner must've deleted your comment" nonsense.