Initially to test a proof of concept I copied themes/contrib/d8w3css/templates/views/views-view-unformatted.html.twig to themes/contrib/mytheme/templates/views/views-view-unformatted.html.twig. Unfortunately after cache-rebuild I still see in the comments that the view refers to the base theme template:
BEGIN OUTPUT from 'themes/contrib/d8w3css/templates/views/views-view-unformatted.html.twig'
Neither changing the name to views-view-unformatted--viewname--displayname.html.twig gives me the expected result. Of course I do "drupal cr --yes" after every change. How to do it right? Or is this somehow a bug?
Fixed
1.13
Documentation
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.