Sucessfully narrowed down to issue to a conflict with the CDN Sync Tool. This plugin has been all over the map and for month we have been using the forked—and by far most stable—version here:
https://github.com/WDGDC/CDN-Sync-Tool
When the plugin is activated along with WP Super Cache's caching enabled, cached pages display on first load, but no content is returned on each subsequent load. When the CDN Sync Tool plugin is disabled, all cached pages load as expected.
Much appreciation to anybody interested in helping troubleshoot this issue. I have posted a issue to the CDN Sync Tool Git repo here:
https://github.com/WDGDC/CDN-Sync-Tool/issues/13
-PaulMighty