Domain Mapping is not working

Domain Mapping is not working on a mapped domain.

For some reason, WPMU DEV staff can't access the site, while the site is working well from my end.

The page showing ERR_TOO_MANY_REDIRECTS.
The front end not loading theme's stylesheet

And the mapped domain is not working.

What have been done so far:
- Deactivated all plugins
- Renamed .htaccess
- Server doesn't block any IPs

Please advise