Go back to your 50 amp plug outside at the pedestal and check that both legs of it are active.
If you have a surge protector/line conditioner, check that power is good on each side of it.
If you have a genset or generator prep package, check the transfer switch for power on both legs of it.
If all is good this far, I would reset every breaker in the panel, main included.
It is possible that one of the receptacle devices has a bad connection. It would be one of the ones in that kitchen slideout, so you may have to check each one for a loose connection. Power off of course.
Lastly, there is a plug up under the belly of the coach. It should be near the flexible wire that you see under the slide that moves with the slide as it goes in and out. That is the junction that transitions from hard wiring to stranded wiring for the slide to be able to
move. The plug has been known to fail.
There is a lot there and if you are not familiar with electricity an electrician is advised. If you like to troubleshoot, follow the path I laid out until you find the cause.
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