I've seen a couple of people ask about this but without a general conclusion.
It worked until recently, but recently all media uploads from the media upload tool end up in an old folder, 2019/10, instead of the one for the current month.
BUT when uploading from a new post, the media goes into the correct folder, for the current month.
So there's different behaviour between uploading from the media upload tool (the stock one), and when uploading from the post editor (the new / Gutenberg one, for blocks).
Any ideas where to start digging?