My left shift key randomly stopped working

I recently sent in my laptop to AppleCare support to fix a few items, and now that I received it back, the left shift key no longer registers when pressed. The right one works fine, along with every other key on my keyboard. I realize I can use the right one, but this is a 2 year old computer and no clue why it wouldn't work anymore.

I did some troubleshooting already like turning on Accessibility Keyboard to see my keystrokes in real-time. Here is where I confirmed that every key is registering EXCEPT the left Shift Key.

2018 Macbook Air, MacOS Big Sur 11.1

Thanks for any help!