When I export VST instrument tracks with different microphone samples on 7-8 output channels to a an ADM BWF file using the internal Cubase functionality, no panning information is included in the generated ADM file.
After bouncing the same tracks to audio all panning is exported correctly.
The panning issue does also not arise when using Fiedler Dolby Atmos Composer in Cubase exporting the same instrument tracks. It also works correctly in Logic.
So I assume it is a bug.