I have a layout with dedicated mix buttons, and a master channel using Bus master and Use Sof.
When I select a send, it works.
If I directly select another send, it disappears.
If I deselect the send before selecting another send, it's visible again.
Also, I have a send button for Main, set to SoF 0.
When I open the program, it's not illuminated.
Once I select it, or select and deselect another send, it is, as it should be.
Same on X Air, Qu, and X32.