Double clicking on gmail username gives me a white page.
Got to Gmail login page and double click on one of the username and before the > arrow, you might have to try couple of times to get this bug.
Its not just gmail, also happening on reddit too, double click a link real quick, you ll see a white page. Looks like this bug activates on double clicking a link.
Same here for gmail… i think this bug comes with last 3 build's of vivaldi.