I’ve tried it. When I am logged into WordPress and not logged into the forum, clicking the login link on the forum is working correctly - my credentials are checked on WordPress and I’m automatically redirected back to Discourse as a logged in user. When I am not logged into either Discourse or WordPress and click the Discourse login link, I’m redirected to WordPress and am able to complete the login process, but I’m not automatically redirected back to the forum. There are a couple of things that could be causing this problem.
I’m not sure what’s going on here. It seems to be working correctly for me. The WP Discourse plugin should not be having any effect on the WordPress login process when a user clicks on a login link from inside of WordPress. If it is, there’s a problem.
I see you have a multisite WordPress setup. It’s possible that some of the trouble you’re having is related to this. Do you have access to the network settings? Do you know if the Network ‘Multisite Configuration’ option has been enabled? It’s purpose is to give all subsites on a network access to the same Discourse forum. It seems like it could be useful for your case. If you have any trouble setting this up, get in touch with me and I can try to help.