S6 Edge (rooted) location information incorrect

Hi,

I am using a rooted S6 Edge (SM-G925FQ)
On location settings , I have enabled wifi, mobile and GPS.
If I am outside, and the phone has GPS coverage, it shows correct location.
If I am inside, and no wifi is available (off), it shows very incorrect location information. (out of my country borders, even 500-600km away)
So it seems that the phone does not show correct location when it uses mobile network.
However, from same location and same settings, my old S5 and S3 show correct location (through mobile network)

is this a known problem with S6 ?
How can I solve this issue ?