Your left/right cable attachment is on the left side of the shifter mechanism underneath, and when you move the shifter left/right it moves and arm and pushes its shift cable forward and backwards. I have seen these deteriorate, my forward/back one was falling apart with a big piece of rubber hanging off the side and it was binding up. I would recommend to pop off the shift handle/cover and see if you can peek down there with a flashlight; otherwise go ahead and take the whole center console off so you can see. I did it and it only took about an hour for my first time. (When I put it back on I trapped the passenger seatbelt end under the center but that's another story...)
It may be as simple as something like that. If your cable end is degraded, then this is the new part that you need:
Transmission Control Manual Transmission
Part number 10 is the cable end for when you move the shifter left/right, and 11 is the cable end for when you move the shifter forward/back.
If you do go in there you might as well replace them both, or what I did was get the whole shifter assembly from the 987 generation boxster, which included the two cable ends as well as all new parts (including bushings etc, already assembled)
99742401000 - Gearshift Bracket For Manual Transmissions - ES#1499714
These may not be the cause but it might be one place to start. If it is from a previous short shifter then you would need to take it off anyway to look at it, so you can inspect the cable ends at that time.
Good luck!
Steve