CB-C71 HUB Ethernet while charging PD port

I have two of these USB-C hubs and have been having all sorts of network problems.
I bought then so I could use MacBook airs with Dell U3419W monitors that supply power over the USB-C display connection. We were originally sending the macbook’s display output through the hub so that we only needed to use 1 of the ports on the laptop, with the RJ45 port connected to our wired network. We also tried plumbing the laptop PSU through the hub.

I realized after a while that every so often, all the devices on our wired network stopped responding one by one over a 30 second period. After unplugging power from the hub, or the hub’s RJ45, our network would eventually recover after a minute or two. I had assumed that something about the powered up transceiver was interfering with spanning tree protocol on our network and gradually causing switch ports to get shut down.

Now we have a rule that the hub stays connected to the laptop and we always disconnect the RJ45.

However - we now have another really annoying problem. Every 3 hours or so the USB ethernet device in these hubs stops being able to send packets, Frequently (and somewhat bizarrely) I can still receive incoming audio, but other traffic (like video, web pages) stop working. After a few minutes MacOS eventually ends up with an ‘auto-assigned IP address’ and no network connectivity.

If I leave a ping running to my router I can see when this happens (several times a day, especially during video concerencing!) The only solution I can find is that hub needs to be unplugged and plugged back in to make things work again.

This problem happens on both MacOS Catalina and Big Sur. It happens with multiple laptops, and it happens with both of our CB-C71 hubs.

This is really frustrating!

Is there any possibility that there is a bug in the Mac USB ethernet driver or firmware? (clearly not shutting down the RJ45 transceiver when the laptop is disconnected seems like a bug - but I’m wondering if there is also some power management issue that is causing the sporadic hangs)

Any suggestions would be much appreciated! (this is making a convenience product more of an ongoing nightmare)

thanks,
Paul