Any idea why boarders of volumes has this artefact?

[abraminmotion]

Here's the file if anyone wants to take a look:

https://www.dropbox.com/s/1icpiqi1yp8q4 ... d.c4d?dl=0

[elsksa]

Perhaps, matching the volume step lengths?

Aside from that, I couldn't help but notice the inappropriate render settings. Check this guide.

[abraminmotion]

Thanks! It appears it was the step length.

Going through the guide now- thanks for that. I'm not sure which settings is inappropriate though. Is there a specific setting that you see that I need to pay attention to? Thanks again!

[elsksa]

I'm not sure which settings is inappropriate though. Is there a specific setting that you see that I need to pay attention to? Thanks again!

It's all on the page, but to name what I've noticed:
- Low Max samples (for final renders at least), in Octane higher values are relatively considered normal than in some other renderers
- Ray depth values are too high (the guide covers that)
- Caustics blur can "safely" be maxed out in most cases, and for any actual caustics need, there is the Photon Tracing Kernel
- GI Clamping is relatively low, although it may work, it's recommended to set it up as per the guide's method

I can't see the settings underneath that upper section, but if VRAM allows, Parallel Sample can be maxed out. The rest is case-by-case and generic shading/lighting/geometry optimization.