Site indexing issue with cache plugin

Hi
I run a site in WordPress with Newsmags theme.
for cache I use lightspeed cache plugin.
yesterday I started posting and everything was ok.
But suddenly my site posts stopped indexing.
my robot txt is ok for indexing.
then I move to cache plugin and press purge everything and my site posts starts indexing again.
I am thinking my site will stop indexing again.
what should I do I can't find why this happening and how to solve this problem.
what is the best setting for lightspeed plugin?
I am not a WordPress developer I need help from expert.