There's a couple things that could be happening, but I'm gonna go with my gut and ask do you have any domains blocked? There's been repeated issues with domain blocking affecting your ability to post (in fact, I had to clear all my domain blocking to properly post to kbin). This is the first thing I'd check.
The next thing would be to see if those instances or communities banned you. This seems unlikely, as it's affecting you on both lemmy.world and lemmy.blahaj.zone. The last thing could be that these communities have defederated or blocked kbin users due to past spam issues (@Technology is still blocked on lemmy.world due to this), but I haven't seen it implemented in this way before.
But I'd start with the domain blocking - 90% of the time when people have problems posting on kbin, that's the cause.