Federation is not perfect between kbin and lemmy. On kbin instances, if the server pulls some federated content that it isn’t quite sure what to do with, it drops it into m/random. Same thing happens if it’s missing any sort of meta data AFAIK
AFAIK it doesn’t go back and update old posts. So if the connection is fixed and the bridge between these two services is rock solid, everything before that won’t be changed. It will only affect future posts.