How to Fix Dropping Indexed Pages in Google Webmaster?

If all of sudden, Google Webmaster start dropping indexed pages of your site, then you are at right place. Read below to know how to fix this problem. To resolve this problem, we had examine all the possible reasons for the decrease in Indexed Pages like
Ensured proper redirect and use of canonical url
Ensured there is no penalty or manual action in the Google Webmaster
Ensured there is no error in the submitted sitemap and
Ensured https links are appearing in the sitemap
But still sitemap’s indexed pages was dropping. This was happeing in both our WordPress site where we recently installed free SSL Certificate.
Of course, we had added both version of websites to Google Webmaster. We had also checked whether ‘http index was decreasing and https was increasing?‘ But this was not the case. There was no such movement.
So what was the reasons for such dropping indexed pages?
Dropping Indexed Pages
The reason was url rewrite http to https after installing SSL Certificate. Yes you heard it correctly. It was https site which was creating this problem.
But if all url are getting redirected to https site then how this could be possible?
It was possible because sitemap url was
Source: https://managewp.org/articles/16660/how-to-fix-dropping-indexed-pages-in-google-webmaster

source https://williechiu40.wordpress.com/2017/11/21/how-to-fix-dropping-indexed-pages-in-google-webmaster/