So I was getting this cache issue with WP Super Cache, where it was refusing to serve the generated cache file. Enabling debug threw this error:
03:39:38 /category/articles/test/ No wp-cache file exists. Must generate a new one.
03:39:39 /category/articles/opinion-columns/ In WP Cache Phase 2
03:39:39 /category/articles/opinion-columns/ Setting up WordPress actions
03:39:39 /category/articles/opinion-columns/ Created output buffer
03:39:40 /category/articles/opinion-columns/ Output buffer callback
03:39:40 /category/articles/opinion-columns/ No closing html tag. Not caching.
Checking the source code on index.php made it clear there was no timestamp on the page, so what the hell?
Referring to this WordPress support thread made it pretty clear something else was interfering with the way the HTML was being generated, so I began disabling my recent plugins one by one.
Lo and behold, the caching test performed fine soon as WP HTTP Compression was disabled. (Not a knock on the plugin by the way, I’m just pointing out what happened.)
Test your cached website by clicking the test button below.
Fetching http://pickandroll.com.au/ to prime cache: OK
Fetching first copy of http://pickandroll.com.au/: OK (1.html)
Fetching second copy of http://pickandroll.com.au/: OK (2.html)
Page 1: 2013-10-05 13:57:49
Page 2: 2013-10-05 13:57:49
The timestamps on both pages match!
And the world was right once more. Kudos to Darrel aka Big Mellz for his sharp eyes on noticing the bug, because it was only happening on the archive pages, rather than the index page, which always seemed to be fine.