Hey there @olsborg,
Do you happen to have any add-ons running? If you have out of date add-ons running, it's possible that they have a conflict with the most recent version of the game and are causing the UI errors.
Try disabling all of your add-ons from the add-on menu then use /reloadui and see if the error goes away. If it does go away, try re-enabling your add-ons until you find the one that is causing the issue, then search the web to see if there's an updated version for patch 1.4.4.
If you continue to receive the UI error after disabling the add-ons, or if you didn't have any add-ons to start with, please us us know.