As a long time user it was time for me to switch to a new phone (android).
After installing the yi home app and logging in all cameras are gone. On the old phone they are all still online, so it seems not to be a user error (deleted cameras).
I am aware yi has still problems with loosing cameras after a firmware update. It is also mentioned on the yi site in case of remote firmware updates. One should power cycle the camera or repair if they are gone. Sure, no problem hop in a car and drive 300 miles to a landhouse to power cycle a camera …
Now I remember why I stopped updating firmwares on the Yi cameras.
Have not encountered such problems with different major and reliable msnufacturers.