Incorrect geolocation in a restored iPhone 6S - how to test, how to check for defects?

Question

iPhone

Yesterday I bought a restored iPhone 6S in DNS, everything is fine, but there may be one problem:
if I run Yandex.Maps indoors (house, shopping center) - it starts not showing my location quite correctly, the point shifts from the real position within a radius of 500-1000 meters.
On the street and in the car - the location is 100% correct.
Nearby in my hands I use the iPhone 5 without a SIM card - with the location everything is exactly the same, without errors.
Is this a geolocation error through a cell tower? Or something with the phone?
Are there any software tools to test the operation of the geolocation mechanism?
Are there any ways to check the operation of the geolocation mechanism in the phone for defects, errors and problems?