Yes, some coaches have devices ahead of the ATS to verify proper shore power.
And, were this device to either be a problem itself OR to deny power to the coach, the check for power IN from shore power at the ATS would reveal a problem "upstream" of the ATS.
Could be a bad CG outlet.
Could be bad power at CG outlet.
Could be problem with the shore power cord.
Could be problem with connection of shore power cord to coach.
Could be problem with a "power monitoring device".
I just find the ATS to be a convenient place to start after a quick visual of the above.