Go to nirsoft.com and download the “USB Device View” tool. Start it on your TC or PC and plug in the webcam. Now write down the ProductID, VendorID, USB class, USB subclass and USB protocol and modify TCX to force this device to map it to a session.
Could be that the webcam is a device with more than one ID set. Maybe because cam and mic are treated separately. Then one part is mapped and the other not.
Add the IDs to the TCX config should fix this.
CG