We were just discussing some potentially-0.19.1-related federation problem that lemmy.today users were experiencing after the update; that’s how I ran across this thread.
The admin there, @mrmanager, restarted the instance again some hours later to attempt to resolve the problem, and it looked like federation started working at that point.
That might be worth consideration if any other instances are seeing problems with posts/comments/votes not propagating.
EDIT: Well, nuts. Now this comment doesn’t seem to be propagating either; visible from lemmy.today but not on lemmy.ml’s Web UI. Maybe if lemmy.today gets restarted again, it will.