Multisite subdomain user logins fail when Domain Mapping plugin is installed

[this is about Domain Mapping but form did not list it as an installed plugin for selection]

Multisite subdomain installed, and everything is working ok.
Wildcard SSL installed and working ok.
User login to subdomain site ok.

Install Domain Mapping plugin, Network Activate it, and users can no longer login to subdomain site over SSL. Disabling Force SSL in wp-config allows login, but that sort of defeats the purpose.

I have deleted and reinstalled domain mapping a few times and each time it is activated user logins to subdomains fail. They get into some sort of loop where they are returned to a login/register screen