The module processes all props through the Drupal render function, which returns a markup object.
If the component's prop has a other type than string this results in the validation error.
We didn't find a better way to resolve this issue than simply converting this prop value to - boolean.
Returning all props as a markup object can cause more problems.
This gave us the idea that it would be good to be able to alter props and slots processed by the module.
Create alter hooks to be able to update props and slots values before passing them to the render array.
Needs review
1.0
Code
I added required changes that give other modules the ability to alter props and slots before they are passed to the render array.
Also, I'm attaching the patch.