As I understand it, you’d be responding to the copy and (after a random amount of time) the comments on each copy would sync.

To drive this home, recent updates to some lemmy instances have caused them to have janky federation issues despite not being blocked. Now and again comments across instances won’t show up or I’ll only get the thread under an image post that for some reason forgot the image when it copied over.

But the original was fine when I checked. I just don’t have an account there in order to comment and it hadn’t synced correctly for me.