This happened yesterday over some swamp-land:

The FPV was cruising nicely (good connection and fresh battery) and suddenly it stops responding to my controls, but I maintain a visual connection and observe it begin the RTH maneuvers. I was puzzled as to what was going on!
I noticed that the values in the OSD no longer showed - for example, the battery percent no longer showed, neither did the height nor distance.
It seemed like some software crashed and the RTH was the fail-safe.

After it landed, I turned everything off and back on again. The drone would take off but the OSD values didn't show - none of the values showed, only the graphics ! So I quickly landed it again.

After a 1 hr drive I was back home and reassembled everything. The headset, controller, and fpv all connected. Without propellers,  I engaged the motors in the apartment and the battery values showed again!

The point is: how can I trust the drone to fly, especially under bridges, when it can suddenly - without warning - engage RTH

Are there any files on the SDcard that I can share to diagnose anything ?

The goggles and the drone both keep a log.
I usually just download the log from the goggles but you will probably want to download the log from the drone as well.

Downloading from the drone is kind of a pain since you need to keep the power on.

Here's a post with more information on this subject.