APM2 and separate GPS unit ?
I'm not certain but I suspect that sometimes my quad is losing GPS lock and maybe that could be due to the GPS receiver being too close to all the other electronics ?
If that may be so then is it possible to either move the GSP receiver so it is on a cable or fit an external unit to replace it ?
In fact, I do not understand why they put the GPS in the middle of the board. There is also heat which can cause problems.
The gps should always be put in such a way radio interference and leakage are minimized. The best is putting it outside the mainboard, or design a perfect radio shield .