Hello!
Your configs look fine overall, but there is quite a bit of unnecessary cleanup/management that could be causing issues.
First, MPF handles all game start/stop logic so you should let the system handle the transition between attract/base modes and back. Manually triggering events to end the attract mode (stop_mode_attract) or simulate the attract mode's internal events (mode_attract_will_stop) may lead to weird behaviors and missed cleanup.
Second, anything triggered by a mode (sounds, slides, lights) will automatically be removed when that mode ends, so you don't need to use mode_<name>_will_end events to do that kind of cleanup. Doesn't necessarily hurt anything, but it will cause noise in the logs and make it harder to figure out what's going on.
Speaking of logs! To your issue at hand, since the configs look good the best thing to check are the logs themselves. From the MPF log, is the event to play the video slide showing up? If not, something's wrong with the configs. From the GMC log, is that event getting heard and the slide being shown?
In the Godot GMC panel there are some options to increase the log levels, BCP and Media will be of the most use. Also when running the game in godot the Scene panel has a Remote/Local option, you can switch to remote to see the actual scene tree of your game in realtime. You can use that to go through the tree and see if your video slide is there, and if so what might be on top of it or why it might not be showing.
Hope that helps!
-Anthony