The temporary fix for this if anybody gets stuck is:
1. Go into FTP and go to wp-content and then within that to plugins,
2. Rename the plugin directory by appending .deactivate to the end.
3. You will then be able to log in as normal.
I’m really disappointed in the maintenance of this plugin to be honest. WordPress core developments are released well ahead of their introduction and with regular monitoring, this issue could have been avoided. I’m doubtful that I will get a reply regarding a fix for this plugin installed on the latest version of WP but i’ll reserve a poor rating for now for later.