Same here. GPS stopped working under Ubuntu Touch just before they gave up and it doesn't work under UBports for MX4 with OTA-11.
Each time I want to use it, I have to wait about 1 hour until unav or Pure Maps finds my location. Even I do not move, I have to wait the same time, when I try it again.
I changed the OS for some weeks to Android/Flyme and it was not much better. Only Google Maps found my place fast by means of WiFi. But all navigation apps failed for at least first 30 minutes of driving.
So I think it's a hardware problem.