Why some pages showing as cached but somes not?

After you enabled LiteMage, you could see most of the pages cached but somes not, such as brand pages.

There are some default system-defined cachable route. Extra routes may need to be added to make the pages cached.

Please check configure of system defined cache route and user defined cache rules.

You can enable debug log and if you see the following:

 
2017-02-21T14:55:31+00:00 DEBUG (7): LiteMage [xx.xx.xx.xx:26072:29461700] ****** PRECHECK route_action [brand_brand_index] /brand/ NO_CACHE=route not cacheable
2017-02-21T15:30:21+00:00 DEBUG (7): LiteMage [xx.xx.xx.xx:37765:19171300] ****** ****** PRECHECK route_action [brand_brand_view] /brand/sorciere.html NO_CACHE=route not cacheable

It means the cache route is not in system default enabled cache route and should be added manually. Go to LiteMage Config→User-Defined Cache Rules→Cacheable Routes. The following would be added: brand_brand_view, brand_brand_index (it may vary if different extension being used, you may need to check your extension code).

Issues can still arise after completing the above steps if the URL is not a standard category or product page as the cached URLs will not be tagged properly. For example, if a product within the brand page is updated, the standard Magento categories and product pages will be auto-purged, but the brand page will not. To resolve this issue, define a custom warm up URL list that will crawl these pages in more frequent intervals, such as every 30 minutes.

Check here for more details.