Cache not working after a few hours

I have a strange issue regarding litemage cache. From time to time, pages become uncached (maybe cache expires ?) and the only solution to fix this is to flush cache storage. When site is slow, cache tags are as following:
  1. X-Frame-Options: SAMEORIGIN
  2. X-LiteSpeed-Cache: miss
After a flush the following tags appear ok :
  1. X-Frame-Options: SAMEORIGIN
  2. X-LiteSpeed-Cache: hit,litemage
  3. X-Powered-By: PHP/5.5.26
The litemage license is starter, and the list size counts 881 pages. The website has 1 storefront, 1 currency enabled.
Magento version is 1.9.0, customized rwd theme
Default Public Cache TTL (seconds) is set at 28800.
Warmup interval is set at 7200.
I can provide debug log and also screenshots from the settings page if needed.

Is there a way to force cache refresh (cron setup maybe) for categories and product pages without flushing ?
Flushing renders the first load of pages very slow (6-8sec for a category page).

Any help is highly appreciated :)
Thanks for the info, will update the license and i'll report back after 1-2 days.

Edit: That was the problem, everything is ok now after licence upgrade.

Thank you !
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