Details
Description
Some blocks' styles.php files are not being included by themes/styles.php.
Specifically, I've been able to produce this bug with the Accessibility block, while other blocks on the page are having their styles.php included.
From what I can tell from the debugging I've done, the stylesheet isn't added to the $files array after the calls to get_sheets_for_plugin_type on line 119.
Ah, here is a guess. Is your block called 'Accessibility' or 'accessibility'? (That is the name of the folder.) It must be all lower-case.