What causes rendered frame "flickering"? Cycles Render. I have a simple scene, with a plane as ground, and objects on it. It is lit by a HDR background texture and one sun lamp, and being rendered to 16-bit TIFF individual frames. The ground plane color begins to flicker a darker version of the same hue after about 240 frames, and then eventually goes to the darker color after a dozen or so flickers over the next 120 frames. The ground material is simple Diffuse BSDF ... What is causing this flicker?

See flickering animation at: https://youtu.be/QSf4CFDx6Zk
It is most likely Z-fighting.
Break down the scene and look if there are any planes in the exact space of orientation.
1 - Could be a hidden object in viewport but still enabled in rendering


2 - Maybe it is an object that is hiding in a different layer.
3 - It could also be 1 object with 2 overlapping faces in the exact same location. (go into edit mode and pull away some edges to check)