This is real but hard fact to as Google gives a tiny ranking boost for HTTPS sites, many sites have begun switching over.But if done incorrectly, it can cause a lot of confusion for your web site listings and rankings in Google.
Google John Muller also replied to a question asked from a SEO on the Webmaster Forum on New Year 2015 .
Question: Google switched over my site pretty quickly from HTTP to HTTPS but then shortly after, began indexing the HTTP version again.
John Mueller, on New Years Day (first Googler to post in the help forums I believe), said this is because the canonical is set on some pages to go from HTTPS to HTTP. That is confusing Google.
Here is what Muller replied on his query :
These kinds of inconsistencies can result in our systems switching back & forth between the HTTP & HTTPS versions; making sure we see consistent information helps us to do what you expect.