When I set up recaptcha v2 in my OJS 3.1.0.1, recaptcha v2 appears correctly, but when it is validate the form, the error that occurs is about recaptcha v1: “Enter the code as it appears in the image”.
Recaptcha v2 has no picture, but only a mouse interaction. Why does this happen and how do I correct it?
I have this same question!!! 
Did you clear you cache system after enable and set recaptcha v2?
Please, check if it fix your issue.
Regards,
Israel Cefrin
Public Knowledge Project Team
Sorry, my server was rejecting external connections, the problem is just that. I released the external connections and everything works normally.