I'm using Huawei P9 for almost 2 years. In my experience, GPS signal with this device is terrible.

After searching Google and XDA I've found that other people also had the same issue with this model. I tried the following steps, works for awhile only.

The steps are:
- Go to "Advance Settings".
- then go to "Location Services"
- Press the 3 dot (on the top right) and select "Scan settings".
- Disable/unselect the Wi-Fi scanning (and "Bluetooth scanning")

I think there is no solution for this phone