Not picking up GPS after tunnel for the remainder of the race (10km-40mins)?!

Hi all,

I ran a 10 miles race yesterday. After +-5.5km we entered into a 300-400m long tunnel. 

The watch just kept on providing laps every 1km as requested, also after the tunnel. These were in line with the distances showed by the organisation next to the track for the first 11k.

However, when the race was over, I saw that the map only showed the first 5.5km, and then just shows data (pace, HR, distance, ... ) until I stopped the activity. See below where you only see the first 5.5km. You do see the elevation for the whole 16k, which seems quiet correct as there was another tunnel at around 14-15km. 

When I look at the TCX file, there are no GPS coordinates past this 5.5km mark. 

What happened?

The watch went automatically to indoor running and did not even try to get a GPS signal after the tunnel? How is this possible? How can I make sur this doesn't happen again?

I have ran this race more than 5 times with several Garmin watches (Fenix 3, Fenix 5, Forerunner 945 and now with the 955) and never had this issue.

I just noticed something really strange, the satellite setting is "off" for the running activity. But if I go outside and start the activity, it gets the GPS signal and finds my location on the map.

When looking to my other activities (biking, snowboarding), the satellite setting is also always "off", although they have been and still are working... ?!?

What is this?