HAPPY UPDATE !I know I was using a different device back then (Xperia X Compact), but in the end it was the same ROM developer and the phones are, from a chip perspective, very similar. The issue you mentioned is exactly the issue I had with the phone, too. Lots of satellites in sight, but no GPS lock, or no GPS lock without waiting for 20 mins.
IT'S WORKING =D !
GPS Test was a wrong app to test Glonass ( it don't work ),
" Harnisch Statut GNSS " is working well ( it's using Open Maps too ^^ )
Actually I've tried it outside my building, without a simcard : localised with a lot of satellites !
But in my building I get nothing : that's just so stupid !
Will lineage Os send my position to google or KGB or what else ?!