@Eosbandi seems to have correctly identified it, we weren’t handling the GNSS config reliably, which was causing us to not fully honor your parameters.
@Anubis you have GPS_GNSS_MODE 1 This means that the GPS is only tracking GPS satellites, and ignores other constellations. What you probably want is GPS_GNSS_MODE 67 which would give you GPS, GLONASS, and SBAS tracking. Which is generally the most predictable coverage. (Depending on where in the world you are you could swap Galileo, or Beidou in if you know you have better coverage there). Don’t enable more then 2 constellations + SBAS however, as an M8 GPS will develop timing issues.