Activity failure & Distance discrepancy

Greetings....

I did a 3 day hike using my 5+ for the 1st time on this type of activity.  Usually use it for cycling activities with no issues.

1st issue was the hiking activity would either reset to 0 or stop completely.  It happened the first day after 5kms by resetting to 0kms then continuing to record.  On the following 2 days I would find that the activity would stop completely and switch back to the normal watch face.  I do have activity lock activated so I need a long press to unlock and pause and did not have anything near my wrist that could have unlocked it by accident.  Would this be due to GPS signal loss or is it a known issue?

2nd issue was there appears to be a distance discrepancy.  I was hiking with my partner who uses a Polar, she had no dropout issues with GPS and logged a greater distance than me on all hikes that I was successfully able to record in full.  On day one allowing for the initial 5km dropout I logged 29km, my partner logged 37km.  On day three I logged 1 x 7km & 1 x 9km whilst she logged 1 x 9km & 1 x 12km.  So as you can see quite a discrepancy.

I did have my app set to record using GPS sat, is this related to again GPS dropout and altitude/descent distance, I am thinking my watch was only calculating flat distance.  Are there better settings to use.....based in the UK if that helps.

Thanks in advance.