Empty left sidebar space when maximizing or snapping window

A month or two ago, I noticed that better touch tool started to reserve some empty white space on the left when I'm trying to maximize a window. I haven't touched or change my BTT settings in years so I'm at a loss what might cause this behavior. Any ideas or help would be much appreciated.

In this screenshot you can see the empty area that's somehow reserved when trying to maximize a window. Not sure it matters but this happens both when I drag a window to the top for maximization or use a keyboard shortcut.