Customers cannot login using email (Failed Login)

Hello,

Recently I started to experience problems with customers logging in using their email address. Every time a customer uses their email and not their username, the login attempt fails. I know this because I’m using a plugin called “User Login History” which tracks login attempts, etc. Interesting enough, I am unable to recreate the issue. But I can’t deny the fact that many customers report the same thing, along with tracking their login attempts.

Any ideas?
Thank you in advance