Extreme latency using Ethernet on Thinkpad X395

A family member recently retired a Thinkpad X395 laptop after upgrading to a Framework 13. I am repurposing that device as a music player for a stereo set.

Since its intended use would have it stationery, I’d like to connect it via Ethernet to get the most stable connection. Since the X395 doesn’t have an ethernet port, I purchased a Thinkpad Ethernet Adapter (shown in the pic below) to use its internal Ethernet controller.
image

When connecting using this Ethernet adapter, everything seems fine at first. Pinging my router gets about 1ms of latency which is expected. However, when I started playing music in Jellyfin Media Player, the ping immediately jumped to 4000+ ms.

The same behavior doesn’t happen when using Wifi.

Yes I know I would be better off buying a USB ethernet adapter and be done with it but I still would like to find out why this is happening.

Laptop Specs:
AMD Ryzen Pro 5 3500U
16GB DDR4 RAM
128GB ADATA SSD
Integrated Vega Graphics
Factory Intel AC-9260 Wifi card
Realtek RTL8111 family Ethernet controller
Linux Mint 21.3 (Kernel 5.15)

Wifi Access Point:
Unifi UAP-AC-PRO

Realtek controllers don’t have an a flawless reputation, you could check for issues as indicated via this post:

https://medium.com/@dawnbreather/fixing-realtek-rtl8111-8168-8411-pci-express-gigabit-ethernet-controller-issues-after-upgrading-to-d7a985ae49ef

This also echoes the overall issue I’ve also seen with RTL8111 on pfsense (driver resets after being put under load, & with hw checksum/offload), though plenty could vary in your device/distribution specifically. I was at least able to solve in software, and seems the above steps solved their problem on a debian-evolved distribution.

There are no logs like what is shown in this post in the output of dmesg. In the dmesg output on my system there are no errors at all.