why does this happen? this is exactly what happened to me, very peculiar and interesting bug haha

There have been many comments with this exact same bug. Haven't found any mention of fix though. Is this in work? I'd love to add this mod but can't live with this bug.
Ah, noticed the author has mentioned they don't own a controller, so I guess we won't see any of the controller bugs fixed anytime soon ;)

OK, my workaround for now is to disable the widescreen fix for just the Equip screen (all other scrrens seem to work fine) by deleting/renaming this file: SteamApps\workshop\content\208580\639641660\override\equip_p.gui
I guess if there ever is a fix, the file will be restored by Steam downloading the fixed version.

On the Equip screen, I can move to the right but not to the left. It's not game breaking, because when you get to the rightmost item and hit right, you loop around to the leftmost item. But it's really annoying. Reproducible with both the d-pad and the left stick.

I had this problem for a while until I found out it was this mod causing it.

Uninstall the Steam version of it and download and install this version: https://deadlystream.com/files/file/332-widescreen-ui-fix-for-knights-of-the-old-republic-2-the-sith-lords/

Have not had a problem since.

The equipment menu should be working correctly now.