I'm not expecting a resolution for this, just confirmation that I'm not going mad!

I bought the 25th Anniversary edition of this game (fancy case, soundtrack etc) and for the life of me I cannot work out why I'm having one weird issue with the left trigger on the Pro Controller. In this updated version for the Switch, the left trigger can be used to draw your gun, and the right trigger to fire. Well, when I hold the left trigger, Conrad starts shuffling to the left, as if left on the d-pad or left stick was also being held.

This issue does not happen with the joycons in handheld mode or in a grip. The Pro Controller works fine with all other games I play, and I've even had it in bits just to make sure there were no issues internally. I've gone through the controller test/calibration just to make sure and everything checked out there too.

So, is anyone else having this issue? I've been searching for days and it's slowly driving me mad.