Yeah, I came here to see if anyone had any insight...

The end seem to make it out that it was kinda all in her head, but doesn't explain the ridiculous scene of what seems to be a ghost using an elevator when the movie already stablished they can float around.

Maybe it was all Ingo messing with her so she would say a ghost did it and she looks cray cray and the police would think she did it.

Could be a combo of both?

Writer/director Assayas messes with our minds, preys on our expectations the same way the mystery texts mess with Maureen. An elevator door & automatic street doors opening and closing imply nothing other than what our imagination cooks up. When you see an automatic door opening by itself in real life, do you assume it’s a ghost? Of course not. Similarly, if you get a mystery text from an unknown number do you assume it’s a ghost? No. But in this movie that’s the conclusion we immediately jump to.

In other words, Assayas tricks us. He first shows us a fictional character (Maureen) who’s so hyper-imaginative that she immediately thinks she’s texting a ghost. We the audience are probably skeptical, and we may even laugh at her for being gullible. But by the end of the movie he has caught us in the same trap. We suddenly assume that a ghost must be using the elevator! (Pretty fricken ridiculous, but we’re all fooled).

The last line of the movie sums it all up perfectly. “Is it just me?” single knock

Assayas shows us, without denying ghosts, that we are easily led to believe in things that don’t exist, but it’s just our own minds. (Or is it? …single knock)