I have an idea of what might have been wrong.
These engines are direct injection so you do not have fuel washing over the intake valves to keep them clean. The valves getting gummed up is a known issue with direct injection. The bigger VW engines use a combination of direct and port injection to avoid it. It's very possible that you suffered a stuck valve due to a buildup of crap on it.
It's tricky. My car is running fine, it's at 65K miles now, but I'm thinking about getting the intake cleaned as a precaution. I may take some stuff off and get a borescope in there to see what it looks like but I don't know how bad the buildup has to be before it's likely to cause a
problem.