I'm experiencing déjà vu. The same comment gets posted twice. I don't know if this is a glitch in lemmy.world's servers (or the servers of a different instance) or if it's just a client problem.
It's most likely a glitch on my end. Most everything I submit to Lemmy has been getting rejected with an error message "cannot connect to Lemmy" So I write the comment again and then later both comments appear.
But I just switched from Sync to Voyager so hopefully I will have a smoother experience with no more glitches.