Pages disappear from Google Search Index after being indexed

I have a website, I use Webmaster Tools for it. I don't use WordPress (it's an ASP.NET website)

Whenever I publish a new page on the site I submit it in WMT > Crawl > Fetch as Google and then click the Index button. This has worked so far for the last year.

My site has in total 960 pages indexed by Google (results of site:[mysite].com)

Recently I noticed that whenever I add a new page via WMT, after half a day it appears in Google searches (both in site: and in a regular search) which is good.

PROBLEM: But then, half a day later it simply disappears both from site: and from the regular searches - not good.

I have no crawling errors, there is no robots.txt problem, no HTML improvements suggested by WMT.

I'm also using a valid sitemap:

• 886 Submitted
• 875 Indexed

What can I do to check what's wrong? Is there a limit on how many pages Google stores for a website depending on it's ranking/popularity?

 

According to my experience, google will auto index every website / page , we only need original content, give some social signal and be sure to ping manually, don't use worthless ping tool . Its take 2 - 3 days until all your page indexed. Or you also add some new backlink to old page

 

I like to suggest you that don't submit your site to the webmaster. Google will automatically crawl your new page. Either you can do Social Bookmarking of the URL or USE the URL in Web 2.0. My strategy will definitely help you out.

 

https://support.google.com/webmasters/answer/40349?hl=en check here