Hi, just got my Mini 9 today. Got 10.5.6 installed and mostly working great.
My WWAN works, but only intermittently. For every time it connects successfully, it will also get into a rut where it won't connect. (Especially after waking from sleep, it seems.)
If I restart, or try again later, without even changing any settings, it will tend to fix itself, and I'll be able to connect fine. However sometimes I'll continue to have a really long string of unsuccessful connection attempts.
Anyway, shout out if this sounds familiar!