Problem with 1 mobile presence, the other works fine

I have a SmartThings location with a V2 hub set up with my main ST account. That location is shared with 2 other SmartThings accounts. Along with various other sensors and switches I have 2 mobile presence sensors, both Android devices running the same software/firmware version. Until roughly a week ago everything was working perfectly, but now one of the two presence sensors will only detect a change in presence if the main account is signed into the SmartThings app. So, if the main account is signed out and the 2 shared accounts are signed in, the arrival or departure of the problem mobile presence sensor is not detected. If the main account is signed in it works great. The other mobile presence sensor works fine with or without the main account signed in. I tried removing the trouble mobile presence sensor and re-adding it, rebooting the hub, resizing the home location circle, everything I could think of. Any ideas where to go next? Thanks…