My main domain is missing in google, subdomain appears instead.

[kevinbp]

I have two SEO optimised pages in my website targeting different keywords

www.example.com                 <-- main selling page (Pocket Guitar | Guitar Instruments)
www.example.com/index/       <-- 2nd selling page (Guitar Australia | Guitar Perth)

Q: At first my website "www.example.com" is ranking on google first page. Suddenly it disappears and the link "www.example.com/index/" appears instead.

No matter what i search, "Pocket Guitar | Guitar Instruments | Guitar Australia | Guitar Perth", the link www.example.com/index/ appears on the front page instead of www.example.com.

What is happening to my main domain? Should i be worried?

[SamuelScott]

I'm getting a sense that you may be suffering from a duplicate-content issue. But first, let me explain.

Duplicate content is not exactly a "penalty" (most of the time). Here's what usually happens: Google sees that two pages of your website are essentially the same, and the search engine does not want to have redundant search results. So, it will usually make a decision to include one of the two in search results (and not the other).

I have to ask: Why do you essentially have two home pages? Is it only to attempt to have the home page rank for two different sets of keywords? If so, then I'm guessing that your two home pages are essentially the same except for some minor keyword variations. It's likely that Google changed its mind (for whatever reason) on which to include and which to ignore.

I'd keep the example.com page as the main home page and 301 (permanent) redirect example.com/index/ to that page. The next time that Google indexes your website, it should see the change and then the SERP should reflect the change shortly thereafter.