I came up with the solution before I finalised this post, so I will post anyway to provide the solution to others, as I hadn’t been able to find it anywhere on here:
SOLUTION:
- Delete plex cookies in your browser.
- Reload Plex browser window and login.
Voila!
Problem below:
I just updated my server and now I get this error whenever I try to play a file in my browser on two different machines:

“There was an unexpected error during playback. Please visit our forums if you continue to experience problems.”
Server Version#: 1.22.2.4282
- Restarting server didn’t help.
- Files will play on other devices and in different browsers with a new sign in.