Within the last month or so, I have started to see a decline in accuracy when tracking workouts using Endomondo on my Lumia 950. It takes ages to get a fix and it only follows movements occasionally resulting in loss of tracked distance.
Endomondo has paused development of their Windows Phone app and the current one does not officially support Windows 10, but it has been working fine for about a year now. I have searched for a way to reset the GPS data in Windows to get it back on track, but there don't seem to be a setting for that.
EDIT: This seems to happen after an update has been installed. Even though the phone was restarted in the end of the update process, GPS fix seems quite random until another restart has been done.