With 30 amp service, the pedestal has only one hot wire. The adapter from 30 to 50 takes the single wire and ties it to both wires of the 50. The transfer switch should still get full voltage from the pedestal to the L1 side of the switch.
A bad 30-50 adapter could be creating a problem.
Also, campgrounds that provide 30 amp only may have older electrical gear or limited power coming into the park. Your voltage at the pedestal could be marginal or might be fluctuating. If it's hot and the park is full, the possibility of voltage drops increases.
If you've had damage to appliances in the RV, you should take some voltage readings at several of your outlets.
Check voltage between Hot and Neutral, between Hot and Ground, and between Neutral and Ground. Ideally you should see 120V, 120V, 0V. If you see readings like 115V, 120V, 5V, you may have a problem with the neutral wiring at the pedestal, adapter, or somewhere inside the coach on the way to the outlets. Problems with neutral wiring need to be investigated to prevent damage to your appliances.