When I’ve mentioned this issue to admins at lemmy.ca and endlesstalk.org (relevant posts here and here), they’ve suggested it’s a misconfiguration. When I said the same to lemmy.world admins (relevant comment here), they also suggested it was misconfig. I mentioned it again recently on the LW channel, and it was only then was Lemmy itself proposed as a problem. It happens on plenty of servers, but not all of them, so I don’t know where the fault lies.