Problems by validating a tooltip of a wpf application

It sounds like a timing issue. Try putting a really long delay between lines 5 and 6 and see if it will run though automatically then. If that works, then you can either try shorter and shorter delays until you find the smallest one that will work, or you can use something like a Wait 

https://support.smartbear.com/testcomplete/docs/app-objects/common-tasks/waiting-process-or-window-activation.html