With #243 we allowed hyphens as pattern id. Although this work perfectly, we haven't fully tested overriding patterns template through theme suggestions.
And indeed if there is a hyphen in the pattern id, overrides are not loaded.
In order to reproduce:
Create a pattern with hyphens in is ID, i.e. this-is-a-test
In your active theme try to override that pattern, creating pattern-this-is-a-test.html.twig template (of course different from content of pattern template!)
Load the pattern in your website, i.e. visiting the Pattern Library section.
With #243 we allowed hyphens as pattern id. Although this work perfectly, we haven't fully tested overriding patterns template through theme suggestions.
And indeed if there is a hyphen in the pattern id, overrides are not loaded.
In order to reproduce:
this-is-a-test
pattern-this-is-a-test.html.twig
template (of course different from content of pattern template!)