I’m having the same issue and Epic support said they can’t help me with it.
I can still access it everywhere, including convert it to a UEFN project, but it’s impossible to edit it directly on Creative.
Still, converting it is not an option to me, since it would remove the ability for players to use their entire jam track inventory due to UEFN limitations
(UEFN project disables JAM LOOPS emote wheel)
Here’s what I got as a response:
"After carefully reviewing, I need to let you know that even though your Island is a published, non-UEFN Island, due to it being archived previously, we don’t have the ability to restore it for you at the moment. "
Careful to not archive any of your Creative 1.0 Islands!