This was my very first thought when I saw the image. The way the damage is closer to the veins than the centre of the leaf panels is a sign too. Water damage would surely be more clustered where the condensation happened, for example where one leaf touched another.
Did you get anything dead?
Mites love humid conditions. The only thing they like more is warm humid conditions. It will be the temps of 19/20 that is slowing them down if anything is.
If it is mites, do not do half measures. If you leave just two mites anywhere they will breed resistant mites that will be harder and harder to kill. I found floramite worked well.
I cropped, cleaned out EVERYTHING and bleached EVERYTHING and threw away and replaced anything that could not be bleached, hoovered every crack, corner, or anywhere that could collect dust, sprayed the single cutting I kept with floramite (then again four days later, then again four days later), also all cracks, doorways, windows, and any access point for something too small to see.
It was effective.
This was after I had a previous infestation where I only did half measures and made my mites resistant to anything that would have killed them before and so because I could not kill them I had to move house...