Check the HVAC controller with VCDS to see if there are blend door actuator fault codes.
The vent output on MK5s is crap when fully operational anyway, imo. There's no appreciable gust of wind from the vent(s) unless you close them all except the one you want.
Whilst on the subject, what is the vent above the hazard light switch for? I've seen other MK5s with just a storage tray there, but mine has what looks like a speaker and a vent knob. Never used it as it makes bugger all difference open or closed