I have Resound hearing aids which can be controlled by the Smart 3D app for IPhone. This also has an app on Apple Watch, which would be really good in theatres etc., EXCEPT that the Watch app only works when the IPhone is switch on with the app running on it. This renders it useless as the phone switches off after a period.
Does anyone have a fix for this?
That s the way all of the apps seem to work, I have given up on the Oticon ON app for that and other reasons. The Apple Watch can now control the volume and programs of MFI hearing aids, but it too needs the iPhone close by.
My phone is in a pocket or shoulder bag for hours at a time when I am out, and sits on my desk at home as I move around doing cooking, cleaning, etc. I change the hearing aid programs from my watch frequently during the day, mostly between All-Around, Music, or Outdoor to quiet noise like the blender or the guy pounding on the new railing on my deck. 
The iPhone screen is off almost the entire time.
Not sure why it does not work for you. (shrug)
2018 iPhone Xs max (iOS 13.3) and Apple Watch 4 (watchOS 6.1)
ReSound Smart 3D app (1.5.1)
2018 Costco ReSound Forte 8 hearing aids (ReSound Linx 3D)
Thanks for the quick replies.
I only have the first Apple Watch and Xr phone, so maybe that is my problem. Both are fully updated but the watchOS is only 4.3.2. Maybe I must wait for a new watch before I can use the functionality.