The "Would you like to force https in login and admin pages:" is stuck in the "No" position. It was in the "Yes" position for many months until I had to make an unrelated change on another option within domain mapping settings. Now it defaults to "No" and has broken the ability for a sub-site user to log into any subsite!
This has happened to other people in the past apparently... https://premium.wpmudev.org/forums/topic/domain-mapping-bug-force-https-setting-in-admin-not-saving?utm_expid=3606929-52.ZpfeUjXqSWOCaoohIqoFQQ.0&utm_referrer=https%3A%2F%2Fwww.google.com
I tried several combinations of Domain Mapping settings and can't get setting to stick. The log-in screen of any sub-site on my multisite has broken SSL on Chrome. Subsite users cannot log in to their sites either. Looking at the html source, it posts to non-ssl version of the site - very bad! Non-sub-site login seems fine though.
I opened my website to support access. Thank you!