ReSound Smart 3d App Syncing on iPhone 15

For some time, my Resound hearing aids pair with my phone but, inconsistently, sync with the app. Sometimes I can re-sync by Bluetooth Off/On. Other times I need to wait for a phone call (sometimes only one is now paired with app). And, sometimes, no problem syncing the HA and app.

I have deleted app and reinstalled at various times, but no help. I do suspect it has something to do with iOS updates, but the HA are almost always paired with the phone, just not the app.