This is happening because the contact between mainboard GPS and antenna located in the back cover is not good.
What I did was to clean very well the contact area, to try to bent a little more outside the GPS antena contact and to add a little aluminum foil in between the mainboard and back cover to ensure a good contact.
I had also another idea in my mind, to install a small piece of wire inside to work like as GPS antenna and to be connected directly to the mainboard to be sure not other loose contacts is ruining the GPS signal