The rumors (I haven't experienced yet, but I am no hardcore Primo user ) are well known: entering a tunnel and having a route set , Primo crashes and GPS device restarts. First one who mentioned it to me was Xtyler92, I believe.
When I remember correctly, he said this happens without exception on several (Chinese) WinCE 5.0 and 6.0 devices, with the original (480x272) data.zip and also with modified data.zips.

These lines in sys.txt should solve this:

[navigation]
use_duration_for_tunnel=1
stop_at_tunnel_end=1

[feature]
tunnel_guidance=0