We had an issue with a freezed HereLink (showed fastboot on the screen and did not react) which still transmitted SBUS signals recently.
I think I have now narrowed the problem down to an issue reported before here: QGC freezes mid flight in Stable Release - #7 by Albert_martinez
So I want to warn everyone who performs long mapping missions and uses camera feedback that this might result in a dangerous freezing of the remote controller.
You can avoid that by regularily restarting QGroundControl during and before each mission.