Electric question

prolly at the connector at the rv side inlet.

When you are having problems, have to checked to see if you have a reading of 220-240V when inserting probes into the 2 hot connections? You should have 120V from either hot connection to ground but something close to 220-240V when probed between the 2 hots.

Happened to me once... History
Original plug on 50 amp cord got nasty so I cut it off and grafted on another (Replacement plug properly applied to cord)
One of the connections in the plug failed.
IF I wiggled the plug (which you did when you switched to the dogbone) the connection would "Make" then later re-fail.

Next stop was the shop for other reasons (Tools I don't have) and while the Technician did his thing.. I did mine with a brand new plug and the cord.. No further issues.

Btax,

If I understand you correctly, you clearly have an intermittent (aka bad connection) that could be just about anywhere. It could be any where along the line.

You changed to another cable and it worked for a while?
Did you check the 50 at the post again?

If any of your cables are not molded end, get out a screw driver and open them up and look for the bad connection.

If you try to diagnose this with a "voltage" detector, that will drive you crazy because there will always be enough AC around to indicate power as there.

Matt

Starting at the shore panel check all connections between there and your RV panel.