I have mydomain.com (which is main site and where WP is installed) and example.com. I noticed that in Network Admin -> Sites "example" (which is mapped to "example.com" and made primary) takes me to example.mydomain.com instead of example.com when I click on dashboard or visit. What I also found that when I put example.com/wp-admin I can log in, manage WP and come back to Network Admin dashboard.
I am almost sure that when I made Multisite WP installation it was ok but now it is redirect me to page which non exist. I didn't touch this. How can I fixed it?