Well, i have the same problem. It only happens on my iphone, not (so far) on my ipad running the same latest IOS. Have tried to delete and reinstall roon remote, but still same behaviour with random crashes (app still running, but in background) very frustrating.
What iOS version do you have on your iPhone? iOS 13.2.2 addressed an issue with apps running in the background, can you check to see if the behavior is still the same after upgrading?