I frequently find this, for some reason kbin.social comments aren’t federating properly. When they reply to my comment thread I am unable to reply to them, and when I log into kbin.social directly and post there my comment doesn’t show up on lemm.ee for some time at all.

Edit: A good fix is to apply a language to your comment, eg English. This should allow your comment to post. However it seems like there is still some issue with comments federating across after that - your comment might appear on kbin, but you might not get their replies again.