Well the same plugin that caused issues with the ability for new users to comment also starting preventing users from logging in to the site altogether, me being one of them. Without naming names, I've decided to move on from this problematic plugin which has restored login functionality to the site.
This also has allowed me to ditch that pretty useless checkbox requirement and implement a less obtrusive login verifier. If anyone is still having trouble logging in, please email the site at [email protected].