First, please try to tap (≠ click) the tweet button seen below. If you use Google Chrome on touch device (such as Android smart phone and Windows-10 touch screen PC), you can tap it. Is this behavior correct ?

The answer is NO. Because a div element with position: fixed; z-index:2 is overlaid on the button with position: relative; z-index:1. The tap to the button should be blocked by the overlay div. For that reason, the button can't be tapped. Actually, such a bug doesn't occur on other browsers (IE, Edge, safari, etc).

The bug only occurs at the top and bottom edges of the overlay div.

Note: There are three SNS share buttons including the tweet button. You can see all of them if you scroll down. The same bug occurs on other buttons, too.

This page is related to Issue 688262.