I've been experiencing the same problem on 20.04 with a different HW setup: Lenovo thinkpad X1 Carbon gen7 (BIOS, thunderbolt controller, etc... firmware all fully up to date), and an Alogic Thunderbolt 3.0 Docking Station.
It generally works fine, but every now and then, the xhci controller in the dock itself stops working causing by webcam to vanish.
Interestingly no other function of the dock stops: DP still works, USB1/2 devices too such as my headset, keyboard and mouse.
It may or may not be the same problem. Next time it happens I'll try capturing the relevant logs.
I've been experiencing the same problem on 20.04 with a different HW setup: Lenovo thinkpad X1 Carbon gen7 (BIOS, thunderbolt controller, etc... firmware all fully up to date), and an Alogic Thunderbolt 3.0 Docking Station.
It generally works fine, but every now and then, the xhci controller in the dock itself stops working causing by webcam to vanish.
Interestingly no other function of the dock stops: DP still works, USB1/2 devices too such as my headset, keyboard and mouse.
It may or may not be the same problem. Next time it happens I'll try capturing the relevant logs.