Bug(?): Renders don't match viewer preview

I'm having a problem with Fusion (within Resolve) where parts of a clip I'm working on are showing up significantly differently when I render the clip; both rendering in place on the timeline and rendering the entire video with the deliver page are giving me the same issue. In this particular case, I'm using a mask to paint out some objects, and I have gotten the composition to look the way I want it to within the Fusion tab. When I move back to the timeline/edit page, the clip still looks the same as it did in the Fusion page after the automatic Fusion render cache process finishes. However, if I then "render in place" the Fusion clip on the timeline, or if I render the whole timeline via the deliver page, I get a darker spot where my mask is. Here's what I mean:

Screenshot 2021-11-10 154719.png (818.67 KiB) Viewed 4693 times

Screenshot 2021-11-10 154658.png (741.03 KiB) Viewed 4693 times

Anyone have any ideas? And more in general, does anyone know why a render would ever look different than the preview in the viewer?

I just noticed something that makes me think this is just a bug. If I render it in place, the frame that the playhead is on when I render it will always be correct. I do realize that the viewer won't update until the playhead is moved though, but I can move it to another frame and then back after the render and it will still be correct. If I then pick a different frame that is for sure busted in that render, I can hit undo to change it back to the Fusion clip, and then render it in place again without moving the playhead. This results in that frame being rendered correctly, despite it clearly being broken in the previous render and not having made any changes to anything other than the position of the playhead.

So hopefully that means I'm not actually doing anything wrong, but honestly it would be much better if I had made a mistake rather than simply not being able to properly render my project. Does anyone have any ideas for a work around, or anything else I could have missed that might actually be the problem?

You could try deleting all render cache for the project...

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If I wanted to see if that fixes the problem without having to leave a bunch of other unrelated clips unrendered, can I just delete that specific clip from the render cache?

Yes, Playback menu -> Delete Render Cache -> Selected Clips.

That didn't fix the issue. I only deleted that clip from the cache, but I can't imagine why it would behave differently if I deleted other clips too. Any other suggestions?