Left stick only moves vertically - not fixed by replacing stick?

Hi there, I have a Vita slim with an issue with the left analogue stick, where vertical movements are registered fine however no horizontal movement is detected. I swapped the left and right analogue sticks and the issue persists, which leads me to believe that the issue is with a ribbon cable or the daughterboard rather than with the analogue sticks themselves. Can anyone help me diagnose this? Thanks!