1: Install Post Type Switcher and Scroll Triggered Boxes (188.8.131.52)
2: Add new box for Scroll Triggered Boxes and save it
Observation: The new Scroll Triggered Box is saved as a "post", not as a "scroll-triggered-box" post type (as expected).
Saving with post type switcher plugin disable a new "scroll-triggered-box" sets the correct post type, so the post type switcher must somehow change the saving logic. I don't know if this is a bug in Post Type Switcher or the other plugin - thanks for a fix though :-)