Registration page does not work properly

[WhyCry]

Hi,

I recently moved my forums to a new server (PHP 5.4->PHP 7.0, Apache to NGINX), and today I decided to test if registration is working properly.

Unfortunately, I found a problem I can't resolve myself. Once 'create my account' button is pressed the page reloads only to tell the user that the username is already taken.

No verification email is sent to entered email addresses either.

The strange part is that new account is added as a member, despite the requirement for email verification. 

Before submitting the form and after:

 

Members are added to the database, despite shown error. Also, for some reason IPs are wrong.

 

I tried to find a solution to this, but nothing seems to work (default theme, clearing cache, repairing database etc.). Neither IPboard error log nor nginx error log are showing any errors. 

Any ideas would be welcomed.