Inconsistent and degrading wired network performance in Ubuntu Desktop

I use Ubuntu Desktop 22.04. I'm experiencing network and internet slowdowns after 30 minutes or so when the wired network is connected. I seem to experience this with both, the built-in PCIe NIC and USB NIC connected via USB-C dock.

This is my work system, and does have Windows installed, but I primarily work in Ubuntu. Windows 10 does not suffer from the same issue. I could leave it running overnight and it's still fine in the morning.

I do not trust the Dell thunderbolt dock, because it is a cheap USB Ethernet controller (included in a $600+ dock to increase their margins I suppose) that does not perform well at all, in any OS as far as I can tell, so I just simply use the Intel onboard NIC on the notebook.

Symptoms:

• Connect to wired network, and go about my business.
• 30 minutes later I notice extremely slow internet and network.
• Toggling the PCIe Network in the GUI will resolve the issue for another 30 minutes or so

This is the only Intel system I have, and I do not seem to experience this on any of my AMD Ryzen desktops or laptop running running same version of Ubuntu Desktop. I do not know if this actually a hardware issue with Dell Precision laptop, or with Ubuntu, or drivers, etc. I would appreciate any suggestions on where to start looking to troubleshoot this.

sudo lshw -C network
...     
*-network
       description: Ethernet interface
       product: Ethernet Connection (14) I219-LM
       vendor: Intel Corporation
       physical id: 1f.6
       bus info: pci@0000:00:1f.6
       logical name: enp0s31f6
       version: 11
       serial: a0:29:19:5a:cf:b1
       size: 1Gbit/s
       capacity: 1Gbit/s
       width: 32 bits
       clock: 33MHz
       capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=5.15.0-58-generic duplex=full firmware=0.4-4 ip=192.168.10.44 latency=0 link=yes multicast=yes port=twisted pair speed=1Gbit/s
       resources: irq:134 memory:b5680000-b569ffff
  *-network
       description: Ethernet interface
       physical id: 12
       bus info: usb@2:1.4
       logical name: enxa02919d88c45
       serial: a0:29:19:d8:8c:45
       size: 10Mbit/s
       capacity: 1Gbit/s
       capabilities: ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd 1000bt 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=r8152 driverversion=v1.12.13 duplex=half firmware=rtl8153b-2 v1 10/23/19 link=no multicast=yes port=MII speed=10Mbit/s

Speedtest results after using the system for a while:

Speedtest results after toggling the NIC in GUI:

Speedtest after 45 minutes of use:

Found the problem (it is a bit stupid), and a workaround. It seems that in this particular system, Ubuntu switches to Wifi, even when the 1Gb Ethernet is plugged in and working. Obviously 2.4GHz Wifi is slow, especially I am far from the access point.

I do not know why Ubuntu does it. It does not do this in Windows on this machine. All I could think of is maybe a wired network issue, but I have verified cables and the switch extensively now (swapped cables between my desktop and this system, ran a new CAT6 cable, borrowed a network tester from a friend and everything physically is good with ethernet). My other laptop does not do this on the same cable. The desktop does not have Wifi, but both desktop and laptop are AMD. Who knows, may be this is a Dell or 11th Gen Intel quirk on Ubuntu. It can also be a driver or network manager bug. Is there logs anywhere that would record this?

Anyways, my workaround is to just turn off the Wifi for now, unless there is a way to find out why Ubuntu switches to Wifi.