Problem with trailing-whitespace face

[leotrs]

When I try to cutomize-face <RET> trailing-whitespace, the following shows

This is of course not the usual window shown when customizing a face.

Furthermore, if I try to customize-face <RET> whitespace-trailing, I cannot find it, the face is not defined. So trailing-whitespace is inheriting from an non-existing face.

This is on emacs 29.3.

Awesome theme btw! Been using it for years.