I have AE v16.1.1 (build 4) and the DXV 3 output installed.
Every time I render out a composition on settings:
- DXV 3
- Normal Quality, With Alpha
Channels: RGB +Alpha
Depth:: Millions of Colors+
Color: Premultiplied (matted)
The background colour renders with it. I had my background colour to a lime green colour. I have toggled the transparency grid in AE and yes the checkered pattern shows and the lime green colour disappears. I know the background should not be rendered with the setting alpha. I have no solids either in my comp.
I think DXV has no chance to screw up things on that side, is just AE.
Check if you're rendering with Premultiplied (matted) instead of straight alpha.
I bet you're premultiplying by lime, tasty but wrong for alpha creation.