Sunroof working only when roof is hot?!

Until about two years ago the sunroof worked all the time, even at -10°C it opened, all of a sudden it started working intermittently until I found out a pattern - if the roof heats up the sunroof works perfectly. So even if outside is cold and I leave it directly under the sun it works (car is black). 

Also worth mentioning if it opens then it works 100% of the time until I shut down the car, I can open/close 1000 times it will work, even if I go in the shade or a cold garage, as long as the ignition is on - but if I shut down the car, and the roof is "cold" , and I start the car up again - no more operating sunroof. I found this out the hard way happily opening the sunroof a few times, parking somewhere colder, coming back and I cannot close it anymore.

Anybody had this problem in the last almost 30 years this car exists on the road and how did you solve it?

Greetings from a 1.8T from 2001. driven till this day, 300.000 km's on the clock, heavily mapped, no oil consumption whatsoever