Issue resolved: I learned that using Leaky Paywall (or any other login option) requires you to switch off WordPress SSO. From Settings > Security, UNCHECK “Allow users to log in to this site using WordPress.com accounts”. Now I am able to log in in an incognito window with my test account; HOWEVER I can no longer edit pages as I had previously (by going to the bottom of a page and clicking “Edit”). When I do this, I get redirected to the login page. I can successfully edit pages from WP Admin, though. Not sure what is going on.