Not about computers but tech.

Recently neighbor from upper flat had water leak in washing machine, and ceiling in my own flat became slightly wet in one room (on places between concrete plates). Leak was fixed, but top electrical line (ceiling lights) got short circuit, and were turned off on electric switchboard. Electrician said that it is common scenario, and I need to wait until ceiling dry up, and maybe then it will start working (or not, depending on wires condition).

So, after few days I've turned electricity on again, and everything was good, Until I've used one switch in that room that controls two LED lamps - they've worked ok, but continued to illuminate even after switching off, just with less light.

First idea was about wrong wiring in switch (not L is switched but N), but it can't happen because that switch worked for 20+ years without problems. Second idea is about current leakage through concrete ceiling that may be still wet inside, but it also looks strange, wiring must be isolated.

What it is may be? Examining wiring is a problematic because it is somewhere inside ceiling (in some tubes), and it is complex task to open it (and also pretty destructive).