i had the same issue
turns out it was a cheap crap 12v usb socket from tesco
no shielded and was cutting the dab constantly
now i just plug the phone into the built in usb on the dash and never lose signal
"" edit"" i have retried with several different 12v things, and i get the same issue with most of them, apart from the fishing lamp that sits on top of the van and plugs into the socket
turns out it was a cheap crap 12v usb socket from tesco
no shielded and was cutting the dab constantly
now i just plug the phone into the built in usb on the dash and never lose signal
"" edit"" i have retried with several different 12v things, and i get the same issue with most of them, apart from the fishing lamp that sits on top of the van and plugs into the socket