Why Google rankings changes if 100 results per page option is used?
Google is always been using this algorithm to make faster outputs.
If a person searching for a keyword with an option 10 results per page, Google algorithm crawls the results through a variety of different data centres that will have very little different cached copies of the index page.
In real-time, there can be a possibility of more than one data centers be crawled during searching, so the result might vary accordingly.
Assume that, if you are using an option 100 results per page, in which the possibility of using more than ten data centers.
So if you do the first search and the data center has your page at 15th position, the webpage will not be in the first ten results.
If you do a second search for page at 3rd position and that data center has your page at 13th position,
Webpage result will not be listed in the second ten results either and you will think that the webpage result has been gone backwards, even though it's around 18th position. Although Google Algorithm takes care of crawling your website, it is highly recommended that the website a person creates should be unique and must have rich contents.
Rich contents, Website Quality and Website Performance makes easy for Google Algorithm understand our website motto as well. Data center is a mediator for Google Algorithm and our website. Through this Data Center, our website got listed in the website ranking result. Above mentioned are some of the common and highly used Data Centers used by Google.