entering to the dashboard of second site in problem

Hi.

I’ve installed multisite on 4.2.4 and domain mapping plugin.
after this added the second site with subdomain and mapped it to another domain on the same hoster. Everything is working well BUT :

when i’m trying to get into second site’s dashboard from main site’s dashboard it’s always redirect me to the same main site’s dashboard. i can get into second site’s dashboard if i’m entering the second site’s dashboard url into address bar manually.

How can i fix it?

Tnx in advance