It's afraid of the cactus.
I noticed that you have it in clay. I found that when I used to grow my orchids in clay, they would do things like this since clay allows so much salt build-up. How long have you had it in that pot, and how often do you fertilize?
I'm not a miltonia expert by any means, but mine don't seem to require too much light, in fact I've read that they prefer slightly shady locations, but not total darkness either. They sure like the water and humidity though.
It's nice and large too, maybe it needs to be divided, then you can send me a piece.
Hi hope it improves with the weather.