Weird Speed and GCrs signals before crashing


I am trying to help a friend to understand a log from a crash.
I have the dataflash log and telemetry log, the first one doesn’t have much information (not saving all data) but it has enought to give some data that seems quite weird to me. As far as I know, those speed and GCrs values make no sense… The increasing oscillation shape of both signals makes me think of a GPS failure. What do you thing?

It seems I cannot edit, maybe I didn’t gave much information (I thought it was irrelevant because the data seemed so strange by itself) lets see if this will help to get an answer…
He was flying an Hexa in auto mode. The hexa had more than 10 flights in auto and some more in stabilize. The mission was an easy one, it was supposed to do a rectangle. Attached is the flight path, the pin indicates when he triggered the RTL.
You can also see the weird oscillation in the Latitude value in the log:
I just need a confirmation that it is as weird as it seems to me, I have recomended him not tu use the GPS but who knows what else can be…