MFA Prompt

Hi All,

Would like to report some issue on our O365 tenant, everytime a user is logging in to O365 they're  prompt with "Additional info required" after clicking Next a page will say "We're sorry, but your Administrator has not enabled you to register at this time" and after clicking cancel it will go directly to their Outlook OWA.

Question is, why MFA is prompting to them even if I didn't enabled it at first? 

I have a Hybrid setup, Exchange 2010 and O365.

Thanks!