I was able to repair this issue but I wanted to post this anyway because it is just so odd.
I've offered free shipping on orders of $150 or more for about as long as I can remember. I noticed that I wasn't receiving large orders over the past several days so I made a test purchase for a few large items and I found that my website was charging customers for orders of $150 or more. I checked the free shipping discount and no changes had been made to it. I haven't made any changes to the discount since it was created 10+ years ago. I checked my shipping settings and everything looked good there as well. I ended up deleting the current free shipping discount and creating a replica of the same discount, and it is now working again. I'm basically just left scratching my head on this one. Why would my free shipping discount just suddenly stop working on it's own without any changes being made to it for the past 10+ years? I'm now wondering if this will happen again at some point(?) Strangeness indeed...