Nighthawk M1

Have had a Nighthawk M1 for probably 18 months but very unsatisfactory.  We use it for mobile broadband with an antenna.  The modem shows the signal to be 'good', but it very rarely actually works.  If I try troubleshooting the problem by running 'network diagnostics',  it often says it cannot find the problem.  Sometimes it does say to restart the modem.

I use satellite internet much of the time (like now) because it is more reliable even if somewhat slower.