Long term damp defo causes problems with corrosion of internal workings of MCbs, switches etc etc. Have been working this week on an electrical supply to 4 flats in a leaking cupboard (leak pointed out 1.5 years ago, but no action taken). Meters (which look ip rated) - knackered. Corrosion on busbar of landlords CU, meter tail blocks - green. But you could definetly feel isolator switches and MCBs are corroded. Ergo would probably not operate correctly when needed. Hence I've ripped out and replaced the lot cos I don't trust any of it. I would also now not be happy to re-connect accessories as per the OP scenario - you can't tell what damage has been done internally.
Ryefield board was also ripped out by western power - guy doing the work was telling me that because they use aluminium for box and some parts inside, the newer Ryefields are prone to internal corrosion in damp atmospheres. The old units made form steel and copper last forever apparently.
