SYNC is in a lot of vehicles (obviously), and a quick google Search turns up a lot of results..
These posts from the F150 Forum maybe helpful?
Couple of Posts from that thread..
"SSM 45917 - 2016-2017 Ford/Lincoln - SYNC 3 – Inaccurate Global Positioning System (GPS) Tracking Or GPS Vehicle Icon Spinning Or Spinning Compass - Engineering Investigating
Some 2016-2017 vehicles equipped with SYNC 3 may experience the following concerns; the GPS not tracking the vehicle position correctly, the vehicle location arrow icon spinning in circles on the navigation screen or a spinning compass on non-navigation vehicles. Perform the following procedure to resolve. Enter BezelDiagnostics per Work Shop Manual (WSM) Section 415-00. Select Testing Settings from the menu. Scroll down and press Clear DR calib. Perform a drive test for approximately 10 minutes, include at least four right turns and four left turns with a vehicle speed of at least 25 MPH. Confirm that GPS position for Navigation or the Compass for non-navigation vehicles is functioning properly. Engineering is aware of this concern"
"Unfortunately, several of us have experienced these symptoms as the start of an APIM failure. First, no GPS, for longer and longer periods. Next, the interface will start getting slower - buttons will take seconds to respond, etc. Eventually, it'll lock up completely.
If that's what you've got, the solution is a new APIM."
These posts from the F150 Forum maybe helpful?
Couple of Posts from that thread..
"SSM 45917 - 2016-2017 Ford/Lincoln - SYNC 3 – Inaccurate Global Positioning System (GPS) Tracking Or GPS Vehicle Icon Spinning Or Spinning Compass - Engineering Investigating
Some 2016-2017 vehicles equipped with SYNC 3 may experience the following concerns; the GPS not tracking the vehicle position correctly, the vehicle location arrow icon spinning in circles on the navigation screen or a spinning compass on non-navigation vehicles. Perform the following procedure to resolve. Enter BezelDiagnostics per Work Shop Manual (WSM) Section 415-00. Select Testing Settings from the menu. Scroll down and press Clear DR calib. Perform a drive test for approximately 10 minutes, include at least four right turns and four left turns with a vehicle speed of at least 25 MPH. Confirm that GPS position for Navigation or the Compass for non-navigation vehicles is functioning properly. Engineering is aware of this concern"
"Unfortunately, several of us have experienced these symptoms as the start of an APIM failure. First, no GPS, for longer and longer periods. Next, the interface will start getting slower - buttons will take seconds to respond, etc. Eventually, it'll lock up completely.
If that's what you've got, the solution is a new APIM."
If the GPS antenna is on top of the dashboard a non-OEM windshield with a metallic film or internal layer, or heating element could interfere. But there are dozens of satellites these days I've never lost coverage other than some long tunnels. I know there are sometimes issues with E-ZPass transponders in some portions of some windshields. 
