Comment 5 for bug 1793965

My suspicion around this is that it's not actually the dock being reset, but rather an MST hub being placed into "high" power mode. The TB16 contains two MST hubs.
The current configuration of monitors you have plugged in probably doesn't exercise both MST hubs, so one of them is operating in "low" power mode.

High power mode spins up the hubs that are off and is needed to query the version of the MST firwmare present on the MST hubs within the dock.

You can confirm this hypothesis like this:
1) Check the fwupdmgr get-devices output as it currently exists. You should probably see 2 MST hubs in the list.
2) Blacklist the "dell" plugin from the fwupd configuration.
3) Reboot the machine
4) Check fwupdmgr get-devieces output.
5) You should probably only see one MST hub in the list.
6) Now unplug all your extra monitors from the TB16.
7) Reboot the machine
8) You should see no MST hubs in the list.

If that hypothesis is correct, then I would say this is actually a kernel graphics driver bug. Intel graphics? Can you please share more on the graphics chipset in use? What model machine you're doing this from?