shift + lmb not adding to selection

Not sure what's going on here, but for some reason after I created another primitive in my scene I can't use shift + lmb to select multiple verts/edges/faces etc.

When I make my new selection with shift + lmb it automatically deselects my old selection.

I'm using Samardac's config if that helps.

You can check the selection hotkey settings.
Edit > Customize > Tools > Common Modeling Shortcut Tools > Exclude Selection, Include Selection, Toggle Selection.