It certainly happened under certain circumstances:
When your website is newly derived and recently updated into the Google search and did not having any inbound links then you need to do
(i) WebMaster tool : submit the sitemap.xml into Google webmaster tool and once you submit then it takes certain time frame to crawl your website as you know so many requests already Google had.
(ii) Google Search Console: If you did not want to add your website into Google webmaster then you can add your website into Google search console.http://www.google.com/addurl.
2.Index tags are missing:
Your website developer can customize it, in order to index the number of pages or to restrict certain pages not to indexed by the Googlebot that’s why certain pages did not appearing in the google search result.
3.Under optimized website:
When you have submitted your website into Google search then Google bots start crawler your website for different- different context such as Title, Meta Tags, Meta description, relevant content, responsive, and how it would be user friendly.
More specifically, its your domain of services as well as products features, those are consumer centric and according you are using the Keyword to target the numbers of user search query. Keyword search and ranking of your website search depending upon the keyword competition as well as traffic. Make sure to choose keyword i.e. having less competitive and more traffic.
5.Website removed from Google Search result:
It has been all depending upon the Google Guidelines under which website must be comprised with all relevant information as per the users’ relevant information. Google might be removed website on certain search on keyword either temporarily or permanently.
Following factors responsible for removal:
(i) De-indexed: Only when your domain removed from Google.
(ii) Penalties: Your website pages did not find through direct search queries and would result into penalty through Google algorithm.
(iii) Sandboxed: even when above both factors did not obliged then it might be possibly removed due to sudden drop in traffic.