iPhone app loses connection after 20-ish minutes

I’ve been using Volumio for quite a while now, and am currently on v3.251, running on RPi with a library of 23k tracks/742GB connected via NFS.

When I use the iPhone app to connect to / control volumio, the app seems to lose connection after 20 minutes or so:
-Open the iPhone app, connect to Volumio, and do some stuff (search for an album and start it playing)
-Thing work fine - i.e. Volumio plays the album as requested from the iPhone app
-exit the iPhone app and either do other stuff on the phone, or just put the phone in my pocket for 20 mins-ish
-open the Volumio iPhone app again
-at this point the app will just show a blank, white screen (note that Volumio is still playing music just fine)
-now I have to force quit the app, re-start it, and select Volumio once again, at which point the app will work fine again

Does anyone else experience this behavior? Or have suggestions on how to resolve it?