Username not being generated from systemUserName from Register User Form

[Pushkar]

Hello,

We are having trouble with the Username generation rules on our Register User Form. We have set an up advanced query for systemUserName generation (based on user's firstname and lastname with various combinations of each), and it is working as expected.

We would like to have two rules for the username generation -
1. username = systemUserName
2. As a fallback, if there is already a user with the same username, username = systemUserName+Auto Increment.

We have set up the username generation rules like so -

However, when we try to create a user from the form, the created username is either blank or a number (from the auto-increment function, probably). In the below screenshot, you can see the username being numbers while the email (which is calculated from the systemUserName) is correctly created.

We have also updated the configuration files as instructed on this thread - 

If we delete the username generation rule altogether, the username is generated as expected, but we need to have the fallback case (auto increment).

Looking forward to any assistance with this problem. Thank you!