Original Post:
https://tri.be/support/forums/topic/single-event-view-not-showing-and-other-generally-odd-behaviour/#post-497192
TL;DR: My template was causing rewrite rules to go missing. I figured that out by disabling all plugins, switching between themes, using the Rewrite Rules Inspector plugin to view/flush rules.
My problem was that the custom template’s functions.php file had a call to “flush_rewrite_rules()” hooked to init with add_action. Simply removing that add_action call and flushing rewrite rules resulted in calendar items displaying correctly. So now the process of rebuilding begins…
Sorry if this isn’t the proper way to follow up a closed thread.