Preload Cache for User Agent Groups

[mavas84]

In some cases, depending on the theme and the environment, cached pages may show the desktop version of the website for mobile/tablet users. In this case, W3TC can create a unique cache for different User Agent Groups in Performance>Cache Groups>Manage User Agent Groups
Enabling groups on mobile and tablet create a separate cache file for these group when the page is visited:

_index_slash_phones_ssl.html
_index_slash_phones_ssl.html_gzip
_index_slash_ssl.html
_index_slash_sl.html_gzip
_index_slash_tablets_ssl.html
_index_slash_tablets_ssl.html_gzip

However, when the Cache Preload is enabled in Performance>Page Cache, the cache is preloaded only for the Desktop version of the website and it only creates the files for the Desktop:

_index_slash_ssl.html
_index_slash_sl.html_gzip

Add the ability to preload the cache for mobile and tablet if the Manage User Agent Groups is enabled. A checkbox in the cache Preload section should be greyed out if the Manage User Agent Groups is not enabled, and is available to check if enabled.

Reference topic: https://wordpress.org/support/topic/mobile-cache-preload/