Screenshot of a single window comes up blank

I followed the instructions here: https://support.apple.com/en-us/HT201361

How to take a screenshot of a window Press Shift-Command-4. The pointer changes to a crosshair. Press the Space bar. The pointer changes to a camera. Move the camera over a window to highlight it. Click your mouse or trackpad. To cancel, press the Esc (Escape) key before you click. Find the screenshot as a .png file on your desktop.

But afterwards, I get a blank image (transparent everywhere).

Has anyone seen this issue, and if so, what am I doing wrong? I am on Sierra 10.12.6

This happens when a window has contents that are rendered outside the windowserver. Mostly 2d/3d, video and modelling software might do this. Some applications do it on purpose, like the Apple DVD player.

I would recommend you use the application "Grab" to take a picture of the screen, window, or selection. Grab comes with all Macs and is located in your "Utilities" folder. The Utilities folder is in with your applications.

Okay, I found out out what's causing it:

I'm using the Honer app https://github.com/puffnfresh/Honer.app, and it interferes with the screenshots, apparently. I've raised an issue about it on GitHub.