Fusion Keys won't export inside Resolve_Crossposting Fusion

I have 4 3 hour art installation projects that are shot entirely on green screen.
We used Fusion to key all of the green.
At times there are 2-4 layers of a keyed green screen on top of one another and the background is always just a solid color.
I can't get any iteration of Resolve to render any of this.
It just crashes while transcoding.
I used to be able to get 30 min of one video to export before crashing,
but now I can't get 4 min transcoded/exported/delivered.

I sent the project to our VFX house so they could try delivering it but to no avail.

These projects are for an artist and are meant to be shown in museums.
This film was supposed to be shown in Norway in April but obviously, COVID set this back.
I would suspect that this ends up showing in person sometime late this year or shows digitally earlier.

This is very stressful as a lot of work and man-hours went into creating this inside resolve and it would be a let down to not find a solution

Post up the hardware in use.

Maybe woth trying prerender the green screen footage to a file with alpha channel before comping them together. If that is not what you did...

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My main workstation is a 10 Core iMac Pro:
Model Name: iMac Pro
Model Identifier: iMacPro1,1
Processor Name: 10-Core Intel Xeon W
Processor Speed: 3 GHz
Number of Processors: 1
Total Number of Cores: 10
Chipset Model: Radeon Pro Vega 64
Type: GPU
Bus: PCIe
PCIe Lane Width: x16
VRAM (Total): 16 GB
128 GB Ram

I have also tried rendering it on a newCheese Mac Pro with better specs than my imac
and I've sent it to a VFX house to try to render all with no avail.