RBR50 with network switch dropping wired connections

Hi folks,

I wired our house for ethernet this summer to support the increased bandwidth uses due to work from home and remote learning.  Most everything is going well and we have a wide variety of devices hanging off the wired connections with great success.  We are having a persistent problem with one machine on the network, a custom-built Windows 10 box.  Whenever this computer is active on the network for a time, it will lose ethernet connectivity and cause almost every other wired device in the house to stop working.  (This is most prominent in our Obi200 interface that bridges our old landline phones into Google Voice.  The phone lines shut down for a while.)  Connectivity comes back after a short period of time, but this is maddening and highly inconvenient.  Devices connected via wifi are unaffected. The problematic computer is plugged into the network switch, but we lose connectivity for everything that's wired, including items plugged directly into the additional ports on the RDR50.  

The setup is as follows:

modem -> Orbi RDR50 |-> network switch -> 7 wired devices

                                    |-> 2 wired devices (TV and Obi200)

                           (via wifi) |-> RDS50 |-> 1 wired device

The first network switch I used was a TPLink TL-SG108.  After reading some posts on the forum about 802.3az protocols built into the unmanaged switch causing issues, I swapped it out for an unmanaged Tenga TEG1008D that does not have 802.3az built in.  In addition, we turned off the EEE/Green Ethernet protocols on the Win10 ethernet adapter side.  Swapped those switches today and still experiencing the issue anytime the Win10 box hits the network.  We have also swapped out the cable between that box and the wall and tried a different wall jack.  Also tried a different ethernet adapter card in case there was some odd short on the motherboard causing the issue.  Results are reproducable every time, although the time-to-drop seems to be relatively variable and there doesn't seem to be a specific type of network access that causes it.  Firmware was standard and up to date, and I've also tried the Voxel firmware with the same outcome.

I'm at my wit's end having worked to troubleshoot this for several weeks.  If the Orbi were still under its return window, I would send it back and start over but at this point, I've sunk substantial cost into the router and accompanying accessories.  Any insights?