Domain Mapping Cross Domain Login Issue

Hello. I'm hosting with WP Engine and having some issues with cross-domain logins. Regardless of using SSL or not, when logged in and using the original domain (subdomain) on the backend and a mapped domain on the frontend, the admin bar doesn't always appear on the frontend due tot he login cookies not crossing over.

The issue is that this doesn't always happen. It seems to work fine for a few weeks, then abruptly stop working. It's inconsistent and hard to reproduce.

The way I've found to fix this issue consistently is to force users to login at the main network domain, then redirect them to their website dashboard upon successful login. I think I remember Donncha's original plugin having this feature. Any chance it will be added to this plugin?