Probably the same issue (or one related) but if I create a thread it generates an error message and does NOT federate to other kbin or lemmy servers, although it does appear on the home instance, kbin.social. However if I upvote the newly created thread it does appear on other servers. It's an annoying bug which I hope is fixed soon, although one relatively easy to work around.
Creating links works fine.
I do not have any domains blocked, so it is not the same as this reported bug (although, again, it appears to be similar or related): https://codeberg.org/Kbin/kbin-core/issues/1019