Thank you for posting! I am sorry things are not working fully as expected while using your Plugable TBT3-UDZ docking station and I would be happy to assist you.
Thank you as well for the excellent detail you have provided and for the thorough troubleshooting that you have already performed that is much appreciated.
Based on your description of the behavior of the dock with both your Dell and MSI laptops, I believe that the cause of the problem is unfortunately internal to the MSI laptop itself. As a result, I am afraid that we will not be able to offer a solution in this specific case.
To expand further, computer manufacturers have discretion when designing Thunderbolt 3 systems in regard to how many external monitors are supported via a single Thunderbolt 3 connection to a Thunderbolt 3 device like the TBT3-UDZ.
Some Thunderbolt 3 computers can support two external monitors via a single Thunderbolt 3 connection to a Thunderbolt 3 device, while other Thunderbolt 3 computers may only support one external monitor via a single Thunderbolt 3 connection to a Thunderbolt 3 device.
I made a video that speaks to this variability and provides additional detail here → https://youtu.be/s0J3ytq29hc
While Plugable does not have your specific model MSI laptop in our test lab, in our experience helping others similar MSI laptop models only supported one external monitor via a single Thunderbolt 3 connection to a Thunderbolt 3 device.
The way to determine how many monitors a specific system supports via its Thunderbolt 3 port (if the manufacturer does not provide this information) is to do precisely what you have done already, in so far as verifying that one external monitor always works regardless of the physical configuration when the Thunderbolt 3 device is connected to the host’s Thunderbolt 3 port.
That one monitor does indeed always work in the scenarios you describe confirms that your MSI laptop only supports one external monitor via a single Thunderbolt 3 connection to a Thunderbolt 3 device.
Given that this is an internal limitation of the MSI laptop which unfortunately cannot be changed, this is why we are unable to offer a solution in this specific case.
Conversely, the your Dell Precision 5560 laptop has Thunderbolt 4 support built-in, as you mention. Any computer that meets the Thunderbolt 4 specification must always support two external monitors via a single Thunderbolt 4 connection to a Thunderbolt 4 or Thunderbolt 3 device. This is why both displays connected to the TBT3-UDZ work properly when connected to your Dell laptop.
You mention, “I used one from another manufacturer and my Dell laptop had USB disconnects and PD issues, so I spent more to get this one, only to find that it doesn’t work with my MSI laptop (the other dock worked fine).”
While I cannot be sure, the ‘other’ docking station you mention most likely was based on a different internal technology as compared to the TBT3-UDZ, which in turn provided for the different result when used with your MSI laptop.
A quick note in this regard, previously you mentioned that you, “updated Thunderbolt and graphics drivers and DisplayLink software”. The TBT3-UDZ docking station does NOT have DisplayLink technology inside of the unit. As a result, it is NOT necessary to install a DisplayLink software driver in order to use the TBT3-UDZ.
With all of that said, we do offer a 30-day no-hassle return policy for all products sold by Plugable and fulfilled by Amazon. If your purchase meets those requirements, then I am afraid that I would have to suggest that you return the TBT3-UDZ docking station to Amazon for a refund.
Apologies again that we cannot offer a solution in this specific case, and thank you in advance for your understanding in regard to all of the technical elements at play!