Heat Pump going out?
I've had worn out 30 amp pedestal connections do that. Be glad your EMS cut out before your plug contact melted the plastic from excess heat. I've seen them toasted black, cracked and distorted and the plug just falls out, they are so bad.
Good idea to have a close look at the receptacle with a strong light before you plug in. If the plug feels loose, that's also a bad sign.
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'The Silver HamShack' (2007 International 22FB CCD 75th Aniversary model)
Multiple Yaesu Radios inside and many antennae sprouting from roof, ProPride hitch
2012 shortbed crewcab 4x4 Toyota Taco TV with more antennae on it