Something strange is going on, but I think I've found a workaround.
- I tried setting a different movie as the background movie.
- In the editor: the original movie still played (not expected)
- In the deployment: the different movie played without an error (expected)
This now leads me to believe that something between the editor and the deployment is trying to play two movies at the same time? Whatever's going on, I successfully got a workaround by making a copy of the title video and giving it a different name.