This is a great little extension, absolutely invaluable to my wiki project, but sadly it doesn't seem to work with 1.24.1. I have restored 1.23.6 for now.
Topic on Extension talk:Spoilers/Flow
I will have to look into the compatibility for 1.24.x. Thanks for letting me know.
Fixed in version 1.3 - https://github.com/Telshin/Spoilers/releases/tag/1.3