Had the same thing happen. I'm assuming one of the sensors broke while doing the timing belt job allowing hot gasses during Regen and melting every thing. Found 2 new sensors and two pigtails on Amazon for roughly 90$ problem fixed.
Chalk up another melted sensor after a TB change. 2015 Passat CVCA - 126k miles. Maybe 60-80 miles after changing the belt, check engine light came on. P2456 code. Cleared it, drove it again the next day and it came back on after about 30 miles.
Opened up the pouch this evening and found it melted and sooty. Expect it'll be replaced under the extended emissions warranty. I did move the pouch and hard lines while doing the TB service. Not much, but apparently enough to do something.
CRUA TB job a couple weeks ago and no melting, but it sounds like it is different than CVCA in layout. I did have to move and disconnect the hard lines in front of the upper TB cover, but did not have to touch the pouch or move those lines much out of the way. At 1000km since and 2 or 3 regens, no problems.
Mine also melted shortly after a TB service that I did. It must not take much movement, as those hard lines were not moved that much. Just enough to get the upper TB cover off, and I typically pry/slide the plastic bracket which holds the hard lines in lace to the upper TB cover away first. I don't remove the DEF injector either, only remove the two coolant lines from the injector, and swing those out of the way.
Dang, I helped buddy with tb change maybe a year back, it was pretty sweltering heat and he had this happen the very next day after doing the job. Had no clue what had happened so got a pair of sensors from Amazon and replaced. So crazy but glad to know it wasn't some freak event, even though he paid to replace them.