Can't play Videos from Web Browser

I've had my Plex Server up for some time and have had no issues until yesterday when I couldn't play videos from a web broswer. I've tried Chrome and Firefox and on multiple PC's. The server loads and I can see all of my media, including new additions, but whatever file I choose to play just gives me the loading circle and never plays.

I can play media fine from Nvidia Shield and from the Microsoft Store App.

Any ideas why this is happening?