I was cleaning wiindows on my wifes MK2 the weekend and decided to try all the windows up and down and put some dry silicon spray on the runners, the front ones get used fairly often but the rears get little use. I tried both front windows and they booth worked fine. Tried both rear windows and neither worked - at first I thought the 'disable rear windows button' on drivers door armrest was pressed, but tried button both ways a few times and neither rear windows worked, turned the radio off and I could hear a faint noise when I tried to open windows so I hit the rear window with flat of my hand and still not good until I started the engine ( a bit extra voltage ) and then the window I had hit went down, had to hit the other window a few times with the flat of hand and it went down as well, sprayed the runners on rear windows liberally with dry silicon and ran them up and down a few times - everything good.
My point is that because of lack of regular use the rear windows can easily stick, and their is very little indication when you press the buttons that window is trying to open, the thing is that all the window motors have a current sensing system, it is mainly to stop the window moving if it sees too much load ( like someones hand or head in the way ), there are no limit switches on the window movement but when window is fully up or down the load sensing cuts the power and stops motor, if window motor sees too much load on the way up it will stop and then reverse if it sees too much load, which is why when you have dirty runners the window will sometimes try to go up but will reverse and go back down if it sees too much load. If windows are stuck in runners in up position the load sensing will cut motor out before they can move.
You may have to resort to my window thumping and running the engine while trying to move the windows and then get some silicon lube on them ( please do not use standard WD40 on them, as it will inevitably attract dirt and stick them even more firmly ), WD do make a silicon lube though.
https://wd40.co.uk/specialist/high-performance-silicone-lubricant/3 in 1 also make a silicon spray, it was on special today at Aldi so I grabbed a couple of cans, long way to come from South Africa to Aldi in UK though.....