Multisite admin login issues with masked/proxy domains

I’m having an issue with users logging in under a masked or proxy domain with a subfolder. But users can login using the main multisite url. For example:

Right now our main url is mainsite.com we have a couple of sites in this multisite environment that live here with both of them masked / proxied to each corresponding site.

site.proxydomain.com points to maindomain.com/subfolder1 – this site have zero issues with when i go to site.proxydomain.com/wp-admin/ or wp-login.php

now this site:
proxydomain.com/subdirectory/ points to maindomain.com/subfolder2 – when i go to proxydomain.com/subdirectory/wp-login.php it redirects to maindomain.com/subfolder2/wp-login.php and when i try to login it just refreshes the page. But when a user goes to maindomain.com/wp-login.php they are able to login fine and go to My Sites > and get to the admin from there.

When i look at the code on the wp-login.php page it looks like it’s trying to submit to proxydomain.com/subdirecotry/wp-login.php so i don’t know if it’s caught in a loop and can’t submit to the masked domain/subfolder.

right now my home and site url are set up as proxydomain.com/subdirecotry/

any help with this issue would be awesome. I’m losing most of my hair trying to figure this out.