So this has been an issue for years by now it feels like.
It's super sporadic, inconsistent and makes no sense to me. it seems to only happen you save as tonemapped png (maybe untonemapped too, but I don't use that). No amount of turning post process, render layers etc off "fixes" it, and also it should work with anything on.
I have had 4 stills where I have had to render one twice and another frame 4 times before it saved and looked correct.
at the same time, as recent as yesterday I had an animation of 300 frames, did a low quality test and sure enough, within the first 20 frames 4 had failed. something to note as well is that it nearly seems to blow up and make things even more noisy when it fails as you can tell by the file size, often 50-100% bigger than what it should be. turned a bunch of stuff on and off over and over, no logic to any of it, ended up having everything on, motion blur, post fx, denoise etc and for some reason this has rendered all 300 frames flawless for 14 hours straight no issues.. but why? it's so flaky and unreliable even when just doing "render current frame" half the time it seems to break.
I don't understand... this doesn't happen with EXR's but that's not the answer nor a solution, there is no reason why png's shouldn't work and also... why can't we save as tonemapped jpegs? again for fast previews or simpler animations where framebuffer looks is fine, why isn't jpegs an option in octane?
phew... anyway I feel like every time I ask other people using octane, they have all had the issue but can't give me a solution. Sometimes people just happen to default to exr only and never see the issue, but it's there. This happens both in the lastest houdini daily build as well as the latest 532 production build... but I had this back in houdini 17.5 as well so..