This is being talked about way too much in multiple threads over the last couple months or os. I suspect a firmware update or mobile app update has created this problem.
There are two fixes to try.
1st - delete camera from app, wait a few minutes, then reinstall it. You must have the serial number of the specific camera to do this. During reinstall, camera goes through a provisioning routine that includes a power reset - equivalent of removing battery.
2nd - If 1st choice didn’t work or you don’t have serial number, remove batteries, wait a few minutes, replace batteries. Write that dang serial # down! Eventually you’ll have all your cameras documented.