What I have tried so far:
- All variations of modifications and additions to .htaccess gzip relevant sections near the bottom.
- The Advanced CSS/JS Aggregation module, and all suggested configurations provided in its readme, which either had no effect or (in the case of the "best pagescore configuration) caused the site to never load until I manually disabled the module.
- All combinations of the above two I can conceive of.
- Disabled all possible competing modules, including adaptive images, boost and core caching of all kinds besides core aggregation required by the Advanced module.
- Threw some junk text into the mod-headers section to confirm it is active and received a 500 error. Repeat result for all relevant apache modules.
The aggregation works fine - whatever configuration I use, save the one that killed the site, successfully produces the aggregate files AND their counterpart gz files and places both in the correct folder under default/files. But come time a page is requested, the server refuses to serve the gz files - it will only serve the full files irrespective of the client's request for compressed files. Could this be a server thing despite the relevant Apache modules otherwise being active? What else is there to try? Could it be on the theme layer or something?