I'm not sure if this specifically applies, but there are federation issues happening across multiple instances.
Many issues have to do with a mismatch in Lemmy BE versions. Lemmy.ml is on 0.18, others are on 0.17.4 waiting for Capcha support to come in 0.18.1. BE 0.18 replaced websockets with http, so it's a substantial update. How this works with kbin specifically I do not know, but things are in flux.
Additionally there is this issue:
https://github.com/LemmyNet/lemmy/issues/3101
Which according to the devs is related to this other issue that has been fixed and will also likely come in 0.18.1
https://github.com/LemmyNet/activitypub-federation-rust/pull/52
So, I do not believe this is international. If lemmy.ml didn't want to federate with kbin they would just defederate. With kbin being its own distinct software that is different than Lemmy, these issues are likely due to the drastic change in the last Lemmy update. Things will have to be ironed out between kbin and Lemmy