Epix Gen 2 huge distance errors

2 of the 4 runs I've recorded have had the distance recorded with huge errors e.g. last night it recorded that I'd ran over 9000 miles.

I think this may be related to altitude being miscalculated for a short period of time.

Garmin chat support were not helpful. They simply suggested a GPS soak, where I'm supposed to leave the watch for 5 to 10 minutes once its acquired its GPS signal. 

I do not live in a built up area and have never had issues with my other Garmin watches. My Forerunner 935 is fine.

This happened with firmware version 6.55. I've now updated to 7.2.

Does anyone know what could cause this and is anyone having similar issues?

Thanks