I have a frustrating problem on two of my multisites that is caused by the Domain Mapping plugin.
Specifically, if the Domain Mapping settings are set to the administration page showing as the "mapped domain" and cross domain login is set to "yes", then if I have logged in to the main site, when I try to view any page of the subsite that has a domain mapped, the page continuously reloads every second, making it completely unusable. This is also true of the login screen - making the dashboard inaccessible.
I have recorded a screen recording showing the exact settings and demonstrating the problem (and also showing how changing the settings off "mapped domain" stops the issue). In the video I have demonstrated this problem with trying to access the backend (dashboard & login screen).
But I forgot that this also affects every front end page on the subsite too, while logged into the main multisite in another tab.
I have this exact issue on 2 different multisite installations. Hopefully this video gives you clear details so that the issue can be troubleshooted. Or if there is possibly something I've setup wrong, please let me know!
I'm using Domain mapping plugin version 126.96.36.199