Thank you.
I was having the same issue.
GPS turned on correctly but maps not keeping up with me or drifting. Direction pointing opposite way etc.
I don’t use my phone on a mount as I have been a passanger in the car with this issue.
Your post made me think what was around me. I use my phone case to hold my bank cards which have a magnetic strip. Once I took my phone out of my case my gps issue was fixed. The magnetic strip must have been interfering with the gps.