UPDATE: Just so everyone knows, this issue has been addressed with multiple changes in this pull-request [1] which is being reviewed by my co-workers and will be merged in the next couple of weeks, then it will be released with version 1.8.8; for the time being, we have implemented some fixes in the server where the API is being hosted, this should resolve the login issues.
Thank you everyone for your patience.
I will mark this as resolved as the main issue has been investigated and a fix has been implemented, if you are still having problems please install the development version of the code [2] or disable the plugin until the next version (which will include all the fixes) is publicly released.
[1] https://github.com/Sucuri/sucuri-wordpress-plugin/pull/40
[2] https://github.com/cixtor/sucuri-wordpress-plugin