My last comment that got voted on, up or down, is from 3 days ago. Could be the same issue. I don't have any other accounts to cross check with, tho.
FYI, you don't need a second account to check, since Lemmy is readable without logging in. All you need to do is navigate to the thread on a different instance. The easiest way to do that is to click on the rainbow federation icon next to the username of comment you replied to.
For example, if I go to your last comment and click the federation icon next next to reev@sh.itjust.works's username, it takes me to their comment on their local instance: https://sh.itjust.works/comment/6737532
As you guessed, your reply does not exist there, because SDF's outgoing federation is busted.
Thank you!
It seems to be broken more frequently than not these days, to the point where I've stopped leaving comments at all for the most part from this account.
Fans of SDF