The changes to the base template lookup in Hugo 0.63.1 mean that the
single/list templates must start with a `define` block. The comment
block that had been in use breaks this requirement and resulted in pages
not rendering properly at all.
See https://gohugo.io/news/0.63.0-relnotes/ particularly:
* Note: In a base template (e.g. baseof.html), the first template block
must be a define.
* Add h-entry microformat markup to single page template
* Add h-feed wrapper around list of articles in list template
* Add h-entry to summary template
In order to improve the semantic layout of the page(s) in the site, the
bulk of the semantic elements have been explicitly moved to the baseof
file. Additional Hugo blocks have been defined to allow layouts to
supply or override things like section menus, the site menu, etc.
Kevin C. Coram