OnePlus 6T Compass Gets "Stuck" Until Placed on Magnetic Mount and Removed

My phone is a OnePlus 6T with Android 11 Oxygen OS 11.1.1.1. I am working on an app which (among other things) provides range and bearing to a particular spot based on GPS and compass. From time to time (every week or so) I have noticed that the compass orientation freezes. I have installed a different compass app and, it doesn't freeze, but it is clearly giving a very wrong reading (for example, north indicated directly to the sun). Similarly Google Maps is showing the wrong reading. I am sure the bearing is wrong because if the sun was in the north we'd be really screwed. Plus I have another compass on my watch and it is OK, so I know where north really is. I suspect the reason my app is frozen, and the other app is not frozen, is just because of the different animation approaches. The root cause appears to be that the sensor is "jammed" even though it is in a solid state. I have tried recalibrating (maybe 40 times), shutting off the phone, resetting the phone, clear the app's memory, stopping the app, etc. I noticed today that if I place my phone on its magnetic mount, all of a sudden the compass started working again once I remove it from the mount. To be clear, I am out in the woods many kilometers away from my magnetic mount when it is jammed, but when I return to my car and put it on/remove it from the mount everything works fine again for a few days. I have never had an electronic compass behave like this. Unfortunately Google searches invariably point me to suggestions to recalibrate.