I had similar issues recently. The copter with Navio2 started showing no sats found despite it being in a clear area. I followed the suggestions made by Sebastion in this link:
In particular I set:
GPS_GNSS_MODE 69 (default 0)
I’m in South Africa so chose this for Glonass, GPS and Galileo. It is and 8 bit field so work out which bits are on - they are described in the parameter tree view in Mission Planner. Then convert binary to decimal.
GPS_SBAS_MODE 0 (default 0)
We don’t have SBAS nearby so I wanted to ensure it was not trying this. [Sebastian had it to 1 for his area.]
GPS_TYPE 2
This forces the uBlox GPS rather than trying to autodetect.
After these changes I am getting 15 to 17 satellites and HDOP is consitently less than 1.
Hope this helps…