Hello,
I tried to create a new designer tab and the tab was unresponsive. I could not design a notification because of that. Please look at the photos to see more.
Hey there @testhong30 
Thanks for reaching out! I’m not running into this error myself. I tried opening a new tab from the designer and it did take a bit to load but it never crashed on me. Please let us know if restarting/updating your browser does the trick, and if this keeps persisting, perhaps a screen recording would help us get to the root cause. Thanks!