You may have already checked this but I'll mention it just in case. Many owners have found the wiring inside the transfer switch box and main breaker panel to be loose or not fully inserted in to screw clamps. Poor connections can cause a lot of intermittent problems. Considering how many wires are in a MH it can be a PIA to check them all but I would start at the beginning, the transfer switch, and work my way out from there. Also might want to check the connections at the back of the shore power plug where your shore line plugs in.
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