Fusion layer won’t render on export

I've got an odd error. I've made a fusion layer that that overlays some particles on top of my video. Straightforward video on V1, fusion comp on V2 with the particles. Particles show up properly in the fusion page. Show up fine in the edit page and preview playback there. Show up fine in the color page. Show up fine in the deliver page preview.

Actual render? No particles.

Added screenshots here, but I’m not sure they'll be informative, as everything appears to be working until the actual export

https://imgur.com/a/fwEoWQ4

I have absolutely no idea where it might be going wrong. I'd appreciate any suggestions.

Did you render out Single clip, or Individual clips?

Whole timeline as a single clip.

This is a pretty basic "Export the final edit" export. Which is why I'm a little stumped on where the issue might be.

I wonder if you could be running out of GPU RAM.

Try forcing CPU processing on all Fusion nodes.

Also, see if you have 'use cache' checked in the deliver page. Either way is fine, but it can screw things up sometimes.

Hi Igor, thanks for chiming in

I've got 8GB of VRAM, which isn't stunning these days, but should be more than enough for what I'm doing. There's not even a dozen particles active at any time

I'm not sure what you mean by "Try forcing CPU processing on all Fusion nodes", if that's an option it's not one I've run across before or something I'm spotting in the manual or with Google searches.

I've since tried saving out the fusion comp in a saver node and I'm getting the same result as the render: show up on the preview but blank on the actual export. So I'm a bit baffled.

And I got frustrated, opened a new project and rebuilt just the fusion comp from scratch. Renders no problem at all. As far as I can tell, every single setting is identical between the two projects, but one renders properly and the other just renders blank. So I got that rendered out and re-imported it as footage into the original project. Dumb, but sometimes you do what works.

At some point I hope Blackmagic takes a full version just for stability fixes.

If you export the comp from the working and non-working projects to files (.comp or whatever the native export format is), can you see any difference ?

Or re-import the working one in the non-working one project ?