Simple Membership Plugin (misc shortcode addon) help

Hello all, so I have set up my membership on my site to when the users account expires it downgrades them to a lower level, where the pages are set to show certain content, I used the misc shortcodes and features to set this up, but i have an issue where if a user logs on with an email, the setting is ignored, but is recognised when signing in with a username, what could be the reason for this? is there a way I can fix this or is there a way to restrict users to not being able to log in with an email but only with username (with passwords). Any advice would be very much appreciated, thank you!