I had the same issue with my vent selector. When I bought mine it barely moved and after pulling the center console I found the cable housing had popped out of it's retaining clamp. That stopped the cable itself from moving within housing and instead the whole cable moved. I was able to loosen the screw for the retaining clamp, slide the housing back into place and tighten it down. While I was in there I did lube up the slide surfaces.
It just happened again this year, but I think because my easypass holder dropped one of it's three suction cups down the defrost vent. When I went to slide to defrost, I felt a little resistance then a pop sound. Now it feels the same as when I bought it, so I'm going back in to fix it.