Can someone help with eGPU weird behaviour in Davinci Resolve

Hello Everyone,

I have a Imac 5K 2017, 4.2Ghz processor, Integrated Radeon Pro 580 GPU, 32Gb Ram, SSD disks and i connected a eGPU to the system a couple of months ago to improve performance in Davinci resolve and all graphic related apps.
The eGPU works great for a lot of apps. In Davinci Resolve, it does make a significant difference when working withNoise reduction and all effects applied to tracks.
HOWEVER, there are a couple of instances where the eGPU does not work.

1 - It does not work with Fusion. Whenever, I use fusion, it only works with the integrated GPU. I have tried several tweaks in vain.
2 - When I render / Export a project, if the eGPU is connected, the system will render via the CPU and not use neither the integrated GPU neither the eGPU. But if I disconnect the eGPU, then the rendering / exporting process will be performed via the integrated GPU. I have tried several combinations into the preferences config of GPU and it is always the same issue. The system does process export via the GPU if the eGPU is connected.

Has anyone experienced the same issue? Do Someone knows a solution for that?

Thanks for your help.