Gang:
I wanted to throw in a couple of observations about this thread.
First of all, the reported main cause of these problems in this thread is poor wiring connections. A little preventative maintenance on the wiring connections in the transfer switch and the generator junction box (if a generator is installed) on any unit that has not had this area inspected would be a good idea. All of the transfer switch connection screws should be tight, and the wires separate to avoid shorts.
Second of all, all of the transfer switches I know of use a large triple pole double throw relay to switch the two live phases and the neutrals between the two power sources and the output to the AC breaker box. This large relay has a set of contacts for each of the 3 wires for each source (6 contacts) with a magnetically actuated contact arm (mechanically returned to the one position by a spring) for each of the 3 output wires. The 3 contact arms have double contacts, one set on each side of the contact arm. These high current contacts are subject to arcing and pitting when switched with loads present: the arcing and pitting can create a poor connection, which when it happens on the neutral feeds can cause the same open neutral - high voltage feeds as an open neutral on an RV park electrical pedestal. THIS MEANS THAT ANY OF US WITH A TRANSFER SWITCH IN OUR POWER WIRING LAYOUT COULD EXPERIENCE THE OPEN NEUTRAL TYPE PROBLEM DUE TO TRANSFER SWITCH CONTACT PITTING. IF YOUR RIG HAS A GENERATOR OR "GENERATOR PREP" YOU HAVE A TRANSFER SWITCH.
The good news is that the contact pitting problem is mostly caused by the transfer relay switching while electrical loads are present. If you don't have or use a generator, the transfer relay is just going to sit in the spring actuated "Shore Power" position ALL the time, never switch, and should not pit or corrode. If you DO use your generator, you can minimize this contact pitting damage within the transfer relay by TURNING OFF THE MAIN AC BREAKERS BEFORE STARTING THE GENERATOR. This will allow the transfer switch to change the contacts connections with no power loads. THEN AFTER THE TRANSFER SWITCH SWITCHES ( I can hear an audible "clunk" inside my trailer when this happens), about 30 seconds after starting your generator, you can turn the AC mains breakers back on. If you use the generator regularly, you may want to service the transfer switch about once a year; removing all trailer power sources, opening the transfer relay box, and using a thin file and contact cleaner/improver spray on all 6 sets of contacts.
Just to clarify my rig's wiring, I had "generator prep" but no installed generator. I installed a battery-powered 1500 watt pure sine wave inverter system and ran the AC power output from the inverter into the "generator" inputs (with the 2 hot terminals jumpered) of the transfer switch. I have a remote inverter on-off switch in the trailer control panel. So my inverter functions as my "generator" and I carry a portable generator in the truck to hook to the shore power cord, if needed.