Hi Andrew, sorry, been tied up with exams this week, and this is a lot different than I thought it was. This is something else going wrong, likely a theme issue, or a loading order issue. Why it is loading all pages, as one, then, dunno... but it seems that memory is being drained somewhere, and caching those section pages seems the logical culprit. It may also be the order of loading that is causing an issue here.
Each section should be small, consisting of a small image, little more than a thumbnail, or two, a line or two of descriptive text under a heading of some sort. In each section are links to one or more pages, one or more activities and resources, quizzes and so on. This is, of necessity, brief, which is why I tend to use labels rather than native section dialogues, for editing sections. The image you have shown us suggests something different. I would think the above method would overcome the necessity of loading each section as a separate page, even if there are 26 sections. You can still use separate pages, but they should load a lot faster.
Fix the section loading problem and this, likely, gives a chance for the rest of the page to load properly.