My dad has a 2014 Skoda Octavia 1.6 TDI, which is a Volkswagen jet in the US. It only has 40,000 miles on it. It has a 6-speed manual tranny that goes bad on the third gear. It kept punching in there.
All the Volkswagen products are notorious for having the shifter bushing problems. So, have the shifter bushings checked. They are plastic and can wear out really fast. If it’s not that, it’s a third gear going out on the transmission. So, you’d want to pray it’s not an internal transmission fault. To verify the problem, I would have a certified technician, such as one from YourMechanic, inspect the car in person. They will be able to diagnose your gear issue and let you know what needs repair.