False duplicate email error during registration

Hello,

I am experiencing an issue with the registration form created with Profile Builder.

When a new user registers with a completely new email address and username, the form shows an error saying that the email/username already exists.

However, the registration is actually completed successfully:

• the user is created in WordPress,
• the confirmation email is sent correctly,
• the user can be found in the Users section.

So it seems that the duplicate email/username validation is triggering incorrectly, showing a false error message after the registration has already been processed.

My registration page uses only the Profile Builder registration form:
[wppb-register]

I am not using any other registration form on the same page.

Could you please help me identify what is causing this false validation error?

Thank you.