Google suddenly stops ranking a page for a "keyword" with same "keyword" in title tag. Low competition.

[vtmoz]

Hi all,

We have released our next version of product called like "software 11", which have thousands of searches every month. So we have just added this same keyword "software 11" as page title suffix to one of the top ranking pages. Obviously this is the page has been added suddenly with "software 11" at page title, multiple header tags and 1 mention in paragraph. Google ranked it for 2 days and suddenly stopped showing this page in entire results for the same keyword we optimised the page for. Why does it happened? Does Google think that we are overdoing with this page and ignoring it?

Thanks