Wow. Sorry to hear what you’re going through. Not much to add, except that children do have active imaginations. Although, as you’ve said, the cumulative number of events seems to rule this out as the only cause.
I would see if there’s a history to this apartment. Or if any of the other residents have experienced something similar. This could be tricky though, as you don’t want to come across as some kook or weirdo. 😉
I don’t have kids myself, but Adam does, so maybe he will have more insights into the magic and mystery of childhood.
At least you’re moving soon, so that’s a positive. Be interesting to see if the events continue after the move, as that would help you narrow down the potential cause(s). Hope it doesn’t continue, by the way. Chalk it up to a weird phase, a story to tell later on, and eventually maybe something to laugh about.