prune_super_cache() deletes too much data due to default cache location

After a night of debugging weird data losses of plugin Autoptimize it became evident, that “something else” outside of Autoptimize deletes all its data including its main cache-folder /cache/autoptimize/ on a more or less regular basis.

This lead to situations where a cached HTML file in client would contain links to currently non-existing .css/.js files on server, so users saw a FOUC page. A reload solved the issue for them, as this triggered Autoptimize to recreated its folder and files.

Finally found that “WP Super Cache” uses WP_CONTENT_DIR . "/cache/" as default folder for its data and when “doing things” with its cache it appears that it also deletes everything inside this folder, including above mentioned cache of other plugins.

Workaround: Added an extra subfolder in “WP Super Cache” advanced settings.

Suggested fix: In future new installs, add an own subfolder within “/cache/” as default.