Precision 3591 won't stay shut down if connected to dock

I just started using a new (to me) Precision 3591 laptop (Ultra 7 155H CPU) with an older Dell docking station (some variant of the WD19, not sure). My previous laptop was a Precision 3551 which worked well with this dock. When I try to shut down the 3591 laptop, if it's connected to the dock (USB-C cable) it goes through the shutdown process but immediately restarts again. In order to shut it down and keep it from restarting, I have to physically unplug the USB-C cable connecting the laptop to the dock before initiating the shut down.

With the old laptop, I could shut it down while still connected to the dock, and it would stay off. Why is the new laptop doing this uncommanded restart when it's connected to the dock? Thanks for any feedback.