random number in every testrun | JMeter Webdriver

I have a script, which create a new user in every testrun with a random number as name. So the users are unique.

But when I start a testrun in Ultimate Thread Group with more than one user it use always the same random-number. Is it possible to create everytime a new one?

I tried to use propertys or reset a variable at the end, but it didn't worked.