Well, there could be a number of problems; things could be biding, kicking on the "pinch protection" feature and then, your window regulator, could be in the process of dying or failing? If the regulator is going bad; you can buy a repair kit from your VW dealer and then, you would need, to tear down the back seat and door panel, to access the regulator, then do the regulator rebuild.
If you have a VW factory level scan tool; like VCDS by Ross Tech, you could scan for codes and read live data, to see if you can narrow down the problem? Failing sensors, can also cause problems or as noted, the window regulators, eventually fail and need replaced or rebuild them with the vw repair kit.