Problem has to be with the receptacle then in the house side... Need to measure them....
Sometimes the ground wires gets not installed and has becomes diconnected some how...
I lucked on my house setup and had an abandoned 20AMP circuit where previous owner had an air compressor setup... This was the only thing being used on this circuit breaker in the house... With the breaker being 20AMPS I got to use more juice haha...
This is going to be a great thing for you to have when camping. lots of times I have run into I needed to power up from a house 15/20AMP receptable. Great to have it all working good...
Try a different receptacle location perhaps but it best to use a tester to know for sure it is wired properly on the house side... Mine only cost arund $10 as I recall from LOWES.
Hopefully your 30AMP shore power plug doesn't look like this one. This is what happens to them when you don't use the lohg DOGBONE type RV Adapter..
Roy Ken