Q: Shared Photo Album Disappeared

I own a shared photo album. Recently the album has disappeared off of all of the invitees' phones, except my own. I have changed zero settings. No one is receiving my invites when I remove them as subscribers and re-add them--have tried emails and phone numbers.  I have cellular data enabled for photos when I don't have access to wifi.  We have not come close to exceeding the 5000 photo capacity. Only have 500 photos thus far. What happened and how can everyone get access to the album again? (Note: I also am unable to turn on the feature "public website"--when I swipe to turn it ON, it automatically switches to OFF.)