So, I'm trying to make this gif for a meme but no matter what I do I guess this swiss cheese looking error and I can't even figure out what the term is to google!
I suspect that you didn't unoptimize the GIF before working on it. In an "optimized" GIF, the frames are transparent were they don't differ from the previous frame, and the successive frames are overlaid above each other (
Of course this doesn't work when you want a transparent background, because the transparency won't cover parts of the previous frame, so you have to go back to
(replace). But the right technique to do this is to use
Filters>Animation>Unoptimize which will produce the correct fully opaque frames by merging in the successive frames.