Operating system: Windows 7 x64
Graphics card: NVIDIA GeForce
Broken: 2.82 a854840e76ae
Short description of error
The new Viewport Render Keyframes operator doesn't recognize Grease Pencil (key)frames, so frames in which the only animation is a GP frame change aren't parsed for rendering.
Exact steps for others to reproduce the error
Open attached blend, play animation, call Viewport Render Keyframes operator, resulting video is not animated.