I've uploaded theme and mysite updates (build on windows local server) to a staging copy of my site on a shared server at Zee-Way.com and neither ?flush=1 nor ?flush=all show any changes on the front end. No errors are shown even when the environment is set to 'dev'. Manually deleting the cache shows no effect either.

Changes to site content and CSS propagate through fine, only the markup seems stuck. I've edited the contents of theme files through FTP and the cPanel with no apparent result after a flush. I even renamed the theme directory so that it couldn't be found and all the markup still came through the front-end after a ?flush=all, the stylesheet and JS file links where just broken.

If I change mysite/config/_config.yml to point to the renamed theme and run a ?flush then everything updates as expected. Editing the theme files and flushing shows the updates right away. Changing the theme directory name and config file back to the original name revert the front end back to that same stuck version.

Where should I try looking to figure out why ?flush isn't producing any result under the original theme name but does under a new one?

Depends on your caching system. Do you have e.g. memcache enabled? Or staticpublisher? Please provide more information about your installation (ss version, possbile modules that may affect caching, do you use partial cache...)

SS 3.1.8, GridField Bulk Editing Tools, Silvergraph, Foundation Forms, GridField Extensions, UserForms, BetterButtons, EventCalendar.

No StaticPublisher. I can't pull a full PHPInfo() with this host but

if(class_exists('Memcache')){}

I re-zipped the theme on my local machine and then uploaded and unzipped it through cPanel (under the original name). After that, flush updated to reflect changes which had been made a few minutes earlier to the copy on the server but not test changes to the freshly uploaded version which overwrote them. I'm currently uploading the theme as loose files through FTP but it's moving very slowly.

Thanks for taking the time to help.

And now flush works.

I stopped uploading the loose theme files by FTP because it had taken nearly two hours to get through barely a third of them (should have taken 2 minutes, literally). Re-uploaded a zipped version and unpacked it in the cPanel file manager. Then changed the site config to point to the newly uploaded copy under its original name, flushed the front end and it all shows up correctly. I modified a template file and the change propagated right through to the front-end without problem.

I have no clue what's going on at this point.

A decent IDE like phpstorm can also upload changed files with ftp, which would make things easier. Maybe your editor / IDE can help you with this?

FTP for this host has been slow the past week or so regardless of what client or user I've used to connect. It's like things hang up on the handshake stage.

I'm still stumped about the caching problem however, especially since I don't even know how to replicate it.