The SCART cable is working fine for the Atari ST.
This first image is using the same cable combination as the first picture in the first post
This is using the SCART cable on the Atari STe.
From what I looked on the pin configuration of both the VBXE and the 1040STe, they should be pretty much the same, I think some of the audio isn’t connected, and the monochrome / high resolution pin, though even that I think works because on the 8-bit it actually makes it go black and white, which I did not expect to happen.
I just updated to firmware 0.79a as well. I haven’t tried the 8-bit since, but the output looks the same on the STe.
These images do go with what you said about AV3, does look like it’s caused do to a filter missing.