Membership 2 problems with default membership and header output


I've got a bit of a problem here, I've got Membership 2 Pro v installed as the only plugin with the Twenty Fifteen theme (previously I had a Genesis theme installed with a lot of different plugins - but the error still persists with no other active plugins and the basic theme)

What I want to do: Create a default membership so that anyone signed into the site after creating an account through any means (woocommerce/gravity forms etc.) can see content. I don't want paid levels and I don't want them to have to choose a membership, it should be automatic on sign up.

From what I understand, the default membership should be best for this but it doesn't seem to be working for me.

When I have Debug set to false in wp-config.php The default membership simply doesn't work. I register a test user with the site and navigate to a protected page I am redirected to the "protected content" page.

When I have Debug set to true and navigate to a protected page then I just get a white page with the following errors:

Notice: Trying to get property of non-object in /xxxx/xxxxxx/wp-content/plugins/membership/app/model/class-ms-model-member.php on line 617

Warning: Cannot modify header information - headers already sent by (output started at /xxxx/xxxxx/wp-content/plugins/membership/app/model/class-ms-model-member.php:617) in /xxxx/xxxxx/wp-includes/pluggable.php on line 1196

There is no white space at the end of my functions.php file or my wp-config.php file.

I have tried resetting Membership which throws up a "Wordpress table xxx_xxxxx.wp_posts doesn't exist" error. It resets the settings but doesn't fix the problem.

I have also deleted and reinstalled Membership but also no change.

Finally I have uploaded a new version of pluggable.php which has also done nothing.

Any help would be appreciated.