Run the exampleSite. The /series/ page is not empty.
Delete this line. Rebuild the exampleSite (you must kill hugo server and re-run it) and refresh the page. The /series/ page will be empty.
Remove mention of .Sections in layouts/partials/paige/subpages.html. Rebuild (re-run) the exampleSite and refresh the page. The /series/ page is not empty.
I have also seen this behavior were using --disableFastRender gets tags page serving correctly (and for me, the issue only affects the server, not building for production).
In my case the suggested
hugo --printPathWarnings
had no warnings, so the issue wasn’t the same as the post I mentioned, but the --disableFastRender did work.
So in my case the problem was that I have WSL2 on Windows and have Hugo binary on both WSL2 and native Windows. In native Windows if I just use hugo instead of hugo.exe it runs the WSL2 binary when I think I’m using the Windows binary and that causes issues (that is when running from PowerShell, running WSL hugo from within a proper WSL2 session works fine).