Complex animation sequence, 1000 frames with linked libraries. Eevee render engine.
Behaviour N°1: I open the .blend file and hit Render Animation; first frame, and only the first frame, renders black & white; all remaining frames render correctly.
Behaviour N°2: I set the viewport to render view. Render view turns out black & white as previous case. Now check this out:
- If I hide/disable in viewport the sun (only light source in my scene) and then I unhide it/enable it in viewport, the scene renders correctly.
- With viewport still in render mode, I move one frame forward and then one frame backward: previously b&w scene now renders correctly.
Behaviour N°3: You hit render single frame (F12). Frame turns out B&W as previously mentioned. Hit render again (Don't update nothing): frame turns out B&W; same behaviour.
With "black & white" I mean all the opaque pixels render 255,255,255; all the alpha pixels render as 0,0,0 with alpha zero.
With "first frame" I mean first frame RENDERED, not the start frame of the animation. I.E: You save the file with the timeline set at the frame #666, reopen file, hit render, frame #666 renders B&W, frame #667 renders correctly
FYI, I uploaded my file to a render farm and I STILL GET THE SAME RESULT! This gives the tip that it is not hardware related.
It's like you have to manually update the scene so that Blender uses the sun lamp. I'm on the dark here guys. I'm really thinking on submitting a bug report