Google doesn't take anymore the exact and fixed title/metatitle and meta description to build the SERP. To build the titletag of the SERP, Google normally mix the metatitle with relevant H1 and H2 in the page, the site name, etc, plus Google builds the SERP titletag dynamically based on the words searched by users. This also relates to how much the metatitle you specified is pertinent to the page contents and to the query of the user searching your page. Metatitle and metadescription are still the most important part of your website to instruct search engines about how to build the SERP snippet, but they are not the only actors, everything is up to Google.
A great video by the Google team to get some more explanations is available at this link: https://www.youtube.com/watch?v=L3HX_8BAhB4
So as a rule of thumb to ensure that Google will follow as much as possible the meta informations specified in your pages, write metatitle and metadescription that are strictly related to the contents of the page and respect the length stated by Google, without exceeding the max characters number.
More interesting informations about meta tags interpretation by search engines can be found here: