base hook preprocess functions not inherited when the theme provides a custom template.

I tried to override a field template template from Display Suite in my theme .. and no output anymore.
Closed because I found out that I have to name the template differently:

not just copy ds-field-minimal.html.twig
but name it field--ds-field-minimal.html.twig

Thats OK, just thought I could simply copy templates form modules to the theme...