Michael777
For future generations, here's how I solved this problem with the help of a Chinese seller:
Try deleting all videos and images saved in the software's internal memory before launching it again. Manual deletion won't help.
Reload the theme's video and configure it.
These settings are located at the bottom center in version 3.1.0.
In the pop-up window at the top, select "internal video" and "internal image" and delete them. Then upload your theme. Everything should work!