XPS 15 9570 and Thunderbolt dock issues

I am beginning to feel that the issue I have just one of those things, and that the cure is a new laptop. 

My primary goal is to run two high res screens off my laptop. Simple enough. 

When I bought my 9570, I had a pair of Dell U3014 monitors. These had happily run at 2560x1600 off a dumb dock connected to my previous laptop. 

I started off with a Dell WD19 Thunderbolt dock back in the Win10 days. From the start I would lose the connection between the laptop and the dock completely - this meant losing video on the two external monitors and also losing the connection to the two external HDs running off the dock. 

Eventually through a series of steps which I cannot remember nor replicate I established a stable connection. Which then one day disappeared, and I went back to losing the connection. 

To explain what that means: Windows makes a ding-dong sound, all three screens go black, wait 5-10 seconds, then the laptop screen comes to life as the only powered screen. Wait a few minutes, and another ding dong sounds and the process reverses. Repeat, every few minutes. Unworkable. 

Since then I have tried (a) a WD22TB dock, (b) an HP G4 TB dock, and (c) and different external screens (currently U2723QE in the office and a pair of generic Chinese 15" 4k screens that can run at 3840x2160. And I have upgraded to Win11. The laptop is powered separately from the dock; at one point I suspected the issue was related to power draws on the laptop during processor-intensive moments, but that correlation no longer holds good. 

Every attempt to run both screens via a TB dock fails. I can leave the Thunderbolt Control Center open on my desktop, and watch it showig a TB dock connected, then show the connection being extinguished, then re-established, over and over again. 

What I can do: run one external screen from the laptop's USB port at as high a resolution as the external screen will manage. I have tried daisy-chaining the U2723QEs (ie avoiding a dock) which seemed like a promising solution, but only the first will run at 4k, with the second at 2560x1600. 

Does anyone - assuming anyone has read this far - know what the cause of or better yet the solution for this is?