Advanced cameras suddenly no longer available in the app

I'm having a problem with my two Netatmo Indoor Advanced cameras. They suddenly disappeared from the app, then I tried to add them again, but that didn't work, and now they're still not in the app and it's telling me to install them as if they were new. But that doesn't work either.

I've tried power cycling them (PoE), but that didn't help. I'm at my wit's end and have to say that so far the cameras have been more trouble than they've needed.