Why is there a website with https in Yandex results?

Question

Search Engine Optimization

Good afternoon!
A strange problem with the issuance of Yandex.
If you type the site address in Yandex, it gives the first link with https, although the site uses the http protocol, and what is most interesting is that this problem does not appear on all computers, that is, it gives someone c http and someone with https

Answer 1

1. This is not a "problem on one computer that doesn't appear on another", but individualized search results for a particular user.
2. Put in robots.txt what is the main site and what is a mirror.

Answer 2

in webmaster select main site with or without www, with or without ssl

Answer 3

Michael, show me the domain, we'll try to figure it out.