The custom folder of the contrabassoon uses F#4+C1-F1 as Activation Sequence. That means, that the notes C1-F1 are note passed along to the synchron player, because Studio 1 treats C1-F1 as part of the activation sequence (keyswitches) not the playing range.
Easy to fix: just delete the custom articulations from the sound variations or change the keyswitches.
Took me some time to find this, so maybe this will help somebody and/or VSL might fix this.