In my experience the tool captures everything initially visible to the user, but doesn't capture any of the screen "below the fold."

Version 59.0.3071.115 (Official Build) (64-bit)
OS Version: OSX 10.11.6

Chrome cuts the screenshots at 16384 pixel height, simple as that.
The PNG spec [1] allows image height of up to 4,294,967,295 so it's a bug in Chrome or in whatever library it uses.

  [1]: http://www.libpng.org/pub/png/spec/iso/index-object.html#11IHDR

Duplicate of issue 719334:

  >This is an implementation limitation deep inside Chrome. I doubt we are going to change that, but I'll leave this bug around in case something changes.

See also  issue 638281 :

  >The 16384px limit stems from the maximum texture size used by the compositor. For GL rendering, this is actually read from the GL context, so a limitation of the GL backend (GPU, software GL, etc.) that can't be changed. For the software GL backend we use with headless, this limit is 16384px. If you're using pure software rendering (without GL support), chromium currently sets the max texture size to 16384px, too. You could change that constant in the implementation to something larger, and run with --disable-gpu to force software rending (I tried this, it does seem to work). But note that software rendering doesn't support WebGL content (and probably also any CSS that requires GL to render correctly).

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Not even showing a warning that the screenshot is cut off is a really bad UX.

As per comment #4 marking it as duplicate for issue 719334, please undo it if anybody feel so

Thank You...