Need help with abnormally long render time

Hello all, I am an intermediate to advanced DaVinci Resolve user and have been using it for the past 2 years to great effect. I normally render roughly 10 minute videos with plenty of fusion effects, compound clips, etc. This on average takes about 20-30 minutes.

I am having trouble with a specific timeline that is taking forever to render a 30 second part of the video.

Here is the deal - I shoot in 4k, and take my images in ~6k, and then render out in 1080p. This has worked flawlessly for me thus far.
The clip in question is an image of a work-desk, where I place cutouts of different tools - such as a box cutter, calculator, pen, etc, then I do an animated colored outline of the tool, and then darken the background items and desk when showing a specific tool(I have to do this independently for each tool or clip below the one being currently shown). To do this - I animate a Color Generator from the OpenFX tools, on each clip, set it to black, and have it go from 0 to .5 opacity, and then back to 0 when the tool returns to the desk. (I had a lot of trouble figuring out a way to do this the way I wanted). I suspect the Color Generator may be the culprit but there are some other things too.

To get the proper cut-outs of the tools, I used a merge node in fusion with a background node set to 1920x1080, and then resized the tool to fit the screen. I did this for each tool.

When rendering, it has crashed many times, and moved extremely slow over this specific area. I believe I have finally figured out how to save it from crashing (by decomposing the compound clip i had it nested in, my first bad experience with compound clips) this is all at the expense of a ridiculous render time.


I am using the free version of DVR

Any advice or help with this situation would be much appreciated.

Here are my PC specs -

Windows 10

32 MB RAM

AMD Ryzen 7 3700X 8-core (16 cpus, ~3.6 GHZ)

Radeon RX 570 Series

VRAM - 8 MB

Update - I did some troubleshooting and was able to find that one of my tool FX (the box cutter) is rendering in place at 20-22 FPS while the rest are rendering at 50-60.

I edited these tools by first opening in fusion - creating a polygon mask to cut out the tool from the background, then merged it over a 1920 x 1080 background - used the merge node to resize it - then copied said polygon mask to create a border mask.

On this tool specifically I have a brightness / contrast node and color corrector node, but removing them doesn't seem to change the render speed. In addition I have a drop shadow added through the edit page, and a color generator to darken the tool when previewing other tools.