This old announcement mentioned that islands can be removed from the island picker/gold rift if it has its star removed from the content service, worth a shot I guess to look for any islands that maybe archived,un-archive them then re-add the star.
For reference the content service link is this https://content-service.bfda.live.use1a.on.epicgames.com/
You can click the star next to the maps name to Re-Star it if it’s unstarred.
Also I don’t think this is a bug but moreso the fact that your islands still utilize your slots, given that unlike deleting maps archiving still “keeps” them, same goes for Converting from FNC to UEFN at any point you can revert it back to FNC so it’s taking a slot.