[Bug / Issue] Errors upon new registrations

[goxy63]

VBulletin version 5.5.0, new members have two strange issues:

1.
When they click "sign up" and they are on page for new registration if they click anything on this page error message pops up and says "Invalid User Name Specified. Username maximum length should be 12 characters." This error is happening only on Google Chrome, on IE I cant reproduce this error.
Check attached image

2.
Dismissing error message above new members are registering and when they are done with registration process they got error message which says "you have been permanently banned by Administrator".
After confirming email address everything seems to be fine.

Any ideas what might be wrong, suggestions?
Recently started to use PositiveSSL "https" and I am not quite sure was this problem there even before that, I did not have any changes recently about registrations so no clue what this might be except upgrading VB5

[goxy63]

https://www.zaliv.net/register

[Wayne Luke]

I can only recreate this issue on your site if the username I enter is indeed longer than 12 characters.

You can adjust the allowed size of your usernames under Settings -> Options -> User Registration Options. The default maximum size is set to 25. This is the maximum number of characters that will fit into the field using the UTF8MB4 character set.