Bonito/sargo are set up like marlin/sailfish and crosshatch/blueline. They share a common folder and some parts of the vendor trees. I think in one of the boardconfigs for sargo, it pulls in the sargo vendor first for the sargo specific for, and then the bonito vendor to get the rest of the common files.
Ah, this does look to be the case. Are you running sargo or bonito?
I wonder if the sargo build isn't linking correctly to the bonito proprietaries. The muppets .mks look a little different from both marlin/sailfish and crosshatch/blueline - the former has proprietaries in each respective folder, while the crosshatch directory alone covers itself and blueline. For the 3a each device has its own directory, but the *-vendor.mk only covers for itself, and in the case of sargo it looks to also need bonito-vendor.mk - but I haven't found where that's linked (or perhaps supposed to be linked) yet.
If you're running sargo I have to wonder if you're missing these files?
Granted, I also only just jumped into this world, so it's easy to jump from one conclusion to another.
I really shouldn't be doing this at work -_-