Well in my case it’s perfectly clear that the problem was defederation because the comments I was able to see with my feddit instance were all there precisely up to the point where a person from lemmy.fmhy.ml, an instance that is blocked on feddit, posted something and everything that was in context of that post was gone when viewed from feddit.
I don’t use many extensions, but apart from the usual UBlock Origin I’ll say something exotic: UltraWideo
Because sites like disney+ still don’t know that 21:9 monitors exist so you have to force it to scale their 21:9 films to your monitor instead of giving you black bars on all sides