I am experiencing an issue on the 13.28 Beta5 and game startup screen for MAME only. After starting a game and then exiting, Bigbox will not start another game. Clicking Play does nothing. I have rolled back to 13.27 and confirmed the issue isn't there and if I turn off the game startup screen option it also works fine. Other Platforms seem to be fine, it just seems to be something with the beta 5 and Mame game startup screen.
Also, the thirdscreen plugin UI now has an error once you open it and then try to close (see screenshot). Once opened you cannot save or close the UI and have to exit bigbox which then won't save your changes. Again, rolling back the build to 13.27 fixes the issue.