Hello,
I reproduced the issue now.
This is because the Output Window contains many lines of text even if you close the Output Window.
You will probably experience the same slow behavior if you try to create a new file (CTRL+N) or open a new file after Step 3.
I will address this issue, but you might want to clear the contents of the Output window (by selecting Clear All on right-click menu in the Output Window) before you close it to minimize this issue.
Thanks!