Xtrons failing to get GPS lock

[RockDriver]

I have a problem with recently installed XTRONS QPB10X5CI unit on my BMW E70. It's failing to get GPS signal lock. Both included and car's GPS (via splitter cable) antennae are connected. The GPS Test app is constantly saying something like "27 in view", but fails to get a 3D lock most of the time. Sometimes it does get a lock with very bad >200 m accuracy and then it drops off again shortly after. I'm trying this under completely open sky, no obstructions, connected to my phone's WiFi hotspot. Any clues as to what could be wrong here?

[RockDriver]

I have discovered the likely cause while having a new dashcam hardwired. One of the GPS wires is broken under the panel not too far from the car's built in GPS unit, but getting to it will require pulling much of the front panel which is like 3 hour job.