iPhone 6 - GPS Not Working.

I purchased a used iPhone 6 in a hurry after my Galaxy S6 went for a swim. The phone works perfect minus the GPS. It will initially find my location, but will not follow with any movement. It might jump around, but typically says "locating". Tried using the compass app and it seems to work well for detecting my heading.

Thought it might be software related so I restored the phone a couple of times and even tried some older firmware. Decided to remove the screen to see if anything was going on and to my surprise it is missing the battery connector bracket (and screws) along with two screws in the LCD shield plate, and the middle screw on the front panel assembly cable bracket. Already contacted the seller without a response.

Other than what I listed the phone seems to be in good overall condition without any major dents or scratches. All of the connectors seem to be seated properly as well. Could the missing screws and cover be causing my issue with the GPS?

Thanks for your help!

UPDATE:

I replaced the missing cover and screws with the ones on my wife's iPhone 6 in addition to swapping the antenna at the top left without any improvement.