Currently it already happen for long time.
I'm using wpmu and have several domain.
web server is nginx
i config to force ssl for admin and login at wp-config.php
maindomain.com is a main site and than put main1.com and main2.com for extra domain that i can choice if create a new site.
and then i make http://www.main1.com as a new site
i can go to https://www.main1.com/wp-admin/
and it's working fine.
sometimes after i updating multi-domain and domain mapping, it do not go to https anymore, a browser will give me a warning about looping.
and than i mark force ssl at wp-config.php and it work.
i see that http://www.main1.com will go to http event i put https at a front.
loop will be happen because of it go to https than http and loop there.
note: i never change any config.
i also want to create a main site for main1.com to have a site without www.
right now i create a new site under main1.com to have http://www.main1.com site
how to make it ?