After creating a new project I have to reopen the programm to create estimate or invoice in the newly created project.

Good day, yuriy.

Thanks for connecting with us. I'm here to address your concern with creating an estimate or invoice and get back things to normal.

A webpage problem might have been caused you from creating an estimate or invoice without reopening QuickBooks Online (QBO). You can rule out that possibility by clearing the browser's cache.

Let's go ahead and clear the cache and see if things start running normally again. Here's a great article that will walk you through the detailed steps: Clear my browser cache and temporary Internet files.

Then, close the browser for the changes to take effect. 

You shouldn't have any further issues after clearing the cache. Please let me know how this turns out. I'm always here to help.