It is an iOS11 problem. I have tried everything suggested by Apple and Resound and nothing seems to cure the dropouts. No Siri. Re - paring the aids from scratch. No other apps running. Resetting Network connections (?), Externally, it could be that MFi is more subject to interference, but since MFi worked fine with iOS 10, it has to be a software bug…
From My Experience (Caveats around) I SEEM to have less problems when I am not using the dedicated Resound hearing aid control app (Smart is what they call it). If I just use Apple’s built in app, That does not make sense to me at all, because the Smart app is just a wrapper for the iOS hearing control. But…
BTW, I found out that the iOS hearing aid control app can be accessed directly from the lock screen with the standard triple tap. This is much better than having to wake up the phone, log in, go to the Smart hearing aid control app, open it then make your adjustments.