I sent the requesting admin from Kbin.earth screenshots and example thread links in DM, and with his or her permission, am sharing the most relevant part of the exchange here for the devs /admins:
Maeve
Compare: https://kbin.earth/m/comradeship@lemmygrad.ml vs https://lemmygrad.ml/1 week ago
blued_gear
I will take a closer look at the issue once I’m back from vacation. What I found in the server logs 'til yet was not very conclusive, except some errors coming from the Lemmy side (but I can’t say if they are the real reason).
Maybe, but it seems somewhat specific to kbin.earth to me. The error logs blued_gear saw might help the right people understand the issue too and dig in further if there’s something that needs fixing either in mbin or lemmy.
The one other mbin instance using 1.10.1 that federates with grad doesn’t have the same issue with the same users at least: