I've been using the Ride with GPS app to record my rides (and navigate new routes). On my last ride, the app paused itself repeatedly—at least seven times—resulting in an inaccurate track. I reported this to RwGPS, and apparently this is a bug created by the iOS 15.2 update, which has affected some other fitness apps as well (the tech support person pointed me to an
article about the same thing happening to RunKeeper). It sounds like keeping the app in the foreground and preventing the screen from locking/sleeping will avoid the problem, obviously at the cost of battery life.
I've also got Cyclemeter on my phone, and will see if that's affected as well. In the meantime, something to be aware of.