As I understand it, kbin was the software boosting every post whenever you clicked the upvote button, while Lemmy uses the bookmark/favorite/star feature which is a lot less disruptive to timeline based clients like Mastodon. Based on that I think Lemmy and Mastodon should interoperate just fine, though you’ll need an app with threading support like Fedilab for comment chains to make any sense.

The software behind kbin has been changed just two days ago so this problem should resolve itself once all the (big) kbin instances have updated their code software.