What's a workaround for Chrome for Android's incorrect clientX and clientY behavior?

Simply use e.pageY - window.scrollY in place of e.clientY (or X, accordingly).

e.pageY will give you where the event happened, and offsetting by window.scrollY will "remove the blank space" that is off-screen due to scroll. You COULD conditional check that e.pageY - window.scrollY === e.clientY, but since the workaround gives you the correct value, and you have to calculate it to check it anyways, that would be counter-intuitive.

I would start by checking that

<meta name="viewport" content="width=device-width, initial-scale=1">

is used. This has fixed a LOT of positional problems in mobile browser applications, particularly with Android. Not sure if it would help your particular problem, but worth a shot.