Issue with shared album

I'm trying to invite someone to an shared album using their iCloud email address. They could previously see the album but for some reason was not able to see recent uploads. So I deleted them and figured I'd just re-invite them.

So far, I've had no luck. When I type their email address, it comes up black not blue. I can add them to the "to" but when I click "add" it seems like they're being invited, but nothing happens. Almost like they are already part of the album and can't be re-invited, but they're not. Not sure how to fix this. This recipient can view my other albums with no issue and has seen earlier photos from this one as well. Very frustrating. Any suggestions? Thanks in advance.