Thanks to EFIDroid I’m able to test things on FP Open and FP OS and while on FP Open GPS works well I seem to suffer from the same issue as you on FP OS:
I do get a fix quite fast and accurately but the curser on the map only jumps to a new position every so often instead of moving along with me.
In SatStat I enabled notifications for GPS fix and for searching, so I can see that the problem seems to be that GPS doesn’t stay fixed.