Steam Controller Input Causing C-Stick Phantom Input

[Klinkin]

For the past few months, I've been unable to use the Steam Input controller option for any game without suffering phantom C-stick input--a hard up and left input, specifically. This occurs whenever the Steam Input option is turned on for any game, and turning it off immediately removes the phantom input.

This behavior is consistent regardless of what controllers I do or don't have plugged in or paired, and I've tried unpairing and repairing my main controller, a Switch Pro Bluetooth controller, repeatedly, to no avail. My other controllers are all via the vJoy driver to connect the official WiiU/Switch GCN-to-USB adapter.

I can confirm that the input is hard C-stick up and left, which normally sends the mouse to the corner of my screen; if I do connect a controller, a hard down-right on the C-stick will hold it still, but I can't get any more from that, leaving games unplayable with a controller.

Has anyone else run into something similar? Does anyone know of a solution? Thanks!