Yes. atuin sync seems to be working correctly. You seem to be doing everything right, AFAIK. If you cannot log back in, then it certainly seems that the issue lies there. One could probably try to investigate, but in this case, it should be easiest to create an entirely new account, log in on both machines, sync everything there, and leave the old account be. IIRC, @ellie does some kind of garbage collecting on the Atuin sync server to remove old accounts that do not update its sync status any more after some X time units. Alternatively, you could ask @ellie to remove the account and allow you to recreate the account again (with the same username, if you so desire).
Instructions for account removal: