On using rails-composer, with the rails-devise-pundit option, I had the following error
Sass::SyntaxError - ".authform form" failed to @extend ".bg-faded".
The selector ".bg-faded" was not found.
Use "@extend .bg-faded !optional" if the extend should be able to fail.
This was fixed using this SO answer. However, I do not understand why it happened in the first place.
Chris