Submit when login or register only refreshes

I’m a bit at a loss. I am most likely overlooking something small but important, but I cannot find it.

I have a few pages that are protected through this plugin, that works. The plugin is set to show the login form if not logged in. If I am logged in through wp-login.php, then I see the page as normal, if I am not logged in, the login form shows.

When not logged into the system, I enter my username and password, hit submit, the page refreshes and continues to show the login form. No WP menu bar on top, no unrestricted pages. Basically it’s a refresh without anything else happening.

The same is true when I use the registration form. After filling everything in, there’s only a refresh but nothing else happens. No new entry in my list of users, no email, etc.

I have looked at quite a few replies and possible solutions on these support forums, I also looked on the rocketgeek.com site for answers, but nothing seems to help. I have seen cache being mentioned quite a few times, but as far as I can tell, there’s no caching going on other than what’s standard in WP. I didn’t install a cache plugin, my host is not using Varnish for me afaik (it’s actually a paid option with my host, I’m not on that plan), so I have no idea what it could be.

Is there anything I am overlooking? Using the wp-login.php works, but as I’m about to accept a few moderators on my site, I was hoping to avoid the WP login and use the WP-Members login instead.