…has the bug that only GPS satellites are used, no GLONASS, no Beidou. You could try one of the latest LOS builds, there the issue is solved and GPS works much better again.
For the upcoming FPOS based on Android 9 they have at least made a copy of the bug in the bug tracker but I don’t know the current status.
So before you start soldering at the core module check the software solutions first 