Steps to reproduce:

1. Go to https://wordpress.github.io/gutenberg/ using an Android device.
2. Tap on the heading content block at the top.
3. Scroll down and tap the (+) icon at the bottom left.

Result: a disorienting screen re-jigger happens. (24s)

Aside: this might be a "normal" Android thing? (I've recently switched from iOS to Android.)

Tested with Chrome on a Pixel with Android 7.1.1.