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If you've crafted nice titles for your blog posts, nothing is more annoying than Google showing another title for your site completely in the search result snippet.
POSSIBLE CAUSES
Wrong title in codeGoogle cache is outdatedSearch term manipulationGoogle ignored the title
Source Code Is Wrong
The source code for your site should contain exactly one title meta tag. If the tag is mission or more than one appears, you may not see the preferred title in search engines. Please view the source code for your site to determine if either of these situations apply.
<title>Preferred title goes here</title>
If you do not see a title meta tag, please follow the steps in this article.
If you have more than one title meta tag, please run a conflict check to determine what other feature on your site outputs the duplicate title(s).
Search Term Manipulation
If you searched for `SEARCHTERM`, Google scans all indexed pages for the exact term or phrase. Google uses the search term to highlight information in search results which is why the meta title is different than what you entered into the plugin.
To see the title without search term manipulation, use the site: search operator followed immediately by the URL of your site. A search for all pages on example.com without search term manipulation would be site:example.com
site:example.com
Google Cache is Outdated
If you've recently updated your title, Google probably hasn't indexed the new title yet. It can take up to a week for Google to index the changes you made, depending on how often your website is crawled.
If you type, in Google, cache: followed immediately by the URL of your site or page, you'll see what Google has cached for your site. If the appeared date is before you made the changes, we'll have to wait for Google to crawl your site again. Sometimes you can speed up this process with the fetch as Googlebot tool.
Search Engines Ignored Your Preferred Title
Google doesn't like your titles. This could be true for all sorts of reasons and the ways of Google are fickle but this article on why Google won't show the right page titles tries to explain it.
Ultimately search engines will, as you have seen, make the final decision on what they show in their search results. Due to this being handled on Google's end, there is little you can do to force Google to display the preferred title. The best advice we can provide, unfortunately, is to try different titles. This article provides advice on crafting good titles for SEO.
https://kb.yoast.com/kb/google...-different-titles-for-my-site/ 
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