Hello Paul,
Possibly will be considered a cheap bodge, but it could be worth spraying some WD40 or similar ( I now used GT85) down the felt window runners - front and back. Partly lower the window before squirting. It might well cure it or it might ease the problem. These window mechanisms are designed to stop closing if there is a restriction, and the restriction may be aggravated by tight runners. If it doesn't work then its doors cards off and see what is going on and if lubrication there might help.
Kind regards,
Gareth,