First two pictures is module just removed from drone (scratches are from my thumbnail).
Normally, siver tarnishing when it come in contact with air. The sulfide is there where the duct tape was removed. No incident. But the previous problems with different GPS modules let think about the mainboard/MCU board. Something maybe wrong there at all.
What let me doubt:
1) Never saw such big difference between telemetry data and reality, even after crash.
A crash is seen at 12:17:00.726 in pitch/roll/yaw. The pos according coordinates and GoogleMaps was here:

At 12:17:01.775 (1s later) Motor 4 off (5-Rotor mode?). And position is that:

At 12:17:01.926 (only 150ms later) last data set before emergency shutdown her:

Next data set is 6s later at 12:17:07.864. Position is now here:

In those 6s everything could happen, but we already lost 1 motor. I think in this gap all the things you described take place (#8). No recording at all. All the time comoass errors that ends with emergency shutdown. GPS accuracy went bad after motor 4 was cut. That's explainable because drone is rotation GPS antenne away from the sky. Also 2.4GHz RC connection got poor.
At 12:17:10:324 the Position shows up here:

Hmm, without running motors? Never ever!
2) With ST16 firmware B25 feature "Dual band Control Redundacy" was introduced. Telemetry (an commands) will be sent either via 2.4GHz ZigBee connection or via 5GHz WiFi from camera hotspot. In the last flight 00353 we see a strange behaviour of the switch of telemetry between 2.4GHz and 5GHz. I never saw such a low and short amout of data from 5GHz. See picture from@WTFDproject:

3) Massive amount of compass calibration warnings during nearly the whole flightlasting over ~22s without interuption. This is also unusual. This may be the main cause of the fly-away.
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