Theme Check will sometimes throw up a confusing warning about how the
style.css file is missing proper information:
RECOMMENDED: Tags: is either empty or missing in style.css header.
It took me a while to figure out that it was caused by more than one file named
style.css in the theme directory. Theme Check applies the tag check to the last file named
style.css that it finds. For example:
mark@caira sheepie $ find . -name 'style.css' ./style.css ./node_modules/html5shiv/test/style.css
Remove or rename any other
style.css files before you run Theme Check.