"That's hard to say because you bought this phone used. That means you (and we) don't know the history of the device. It may have received several impacts over it's life, or been exposed to water or even previously repaired. The more we know about the phone, the better.
It could be antenna related or it could be logic board related. Ultimately, this phone needs to be opened up and inspected. First you isolate the easier, modular issues (antenna, connectors etc) and then you look at the logic board itself. Take a look at this guide."
I think the no gps fix started around ios10 and lasted till now. But when i was fiddling with my mail settings, noticing the odd | new data: ‘push’ | option at the bottom of the accounts and password page in ‘settings’. . Could that be the culprit? I flipped the switch and instantly gps had a location fix.
So: to turn on gps location fix just flip ‘push’-button to ‘on’ under settings - accounts and passwords’ - new data : push>"
