I'm using X1E (1st gen).
At work I connect it to TB3 dock (OWC), and not a single problem so far.
At home I connect it to one small usb-c hub, and as in previous example, not even one problem with it.
Now I own X1C, but that one my wife uses. She doesn't connect any tb3/usb-c devices into it, so if there is an issue with that device, I'm not aware of it. But I will test it out for sure.