Random noisy frames

I am having trouble with E_Render producing noisy /low sample images randomly in the middle of a render, like in these consecutive frames:

I tried resetting the cache and tweaking random values. Sometimes it snaps back to being nice and smooth but then other random frames seem noisy.

What could be causing this?
Nuke script attached (the bottom two frame hold nodes produce the above screen shot)
eddy_render_issue.nk (184.1 KB)

This is most likely due to the automatic render settings deciding to use a different integrator when the characteristics of the volume change. It’s easy to fix, just enable the ‘custom settings’ in the E_Render node. This will use those settings consistently instead of automatically choosing. The default settings should be okay, maybe just enable the supervoxel option.

great, thank you, I will try that next time.