Slow Ethernet on Dell c3422we monitor, fine with connected adapter

I've been troubleshooting a weird issue for a few days. I have a 2021 14-inch MacBook Pro M1 Pro with 16GB RAM running Sonoma 14.5. I also have a Dell c3422we monitor, and have installed the Dell Display and Peripheral Manager (latest version - 1.3.1.0015). I connect to my monitor using only one cable, USB-C, which also delivers power.

I get slow ethernet using the built-in ethernet connector - ~60mbps down, 50mbps up. I connect using an Anker USB-C to USB-C 3.1 cable. Using wi-fi, I get ~400mbps down. I tried troubleshooting various monitor settings, using separate power delivery, etc. During my searching, I found that sometimes, Apple doesn't behave nicely with the realtek 8153 chip in my monitor, and that Dell distributes an updated driver for Windows.

This is how the ethernet adapter displays in System Information:

To test my ethernet cable and connection, I plugged in an Aukey USB C Hub that includes Ethernet, 4K HDMI, VGA, 2 USB 3.0 type-a ports and 100W charging. directly to the Mac. I got ~600 mbps down.

To test further, I connected the Aukey to the monitor, and plugged Ethernet into the adapter. I get ~600mbps down through the adapter connected to the monitor. It uses the same driver and has the same chip as the Dell monitor.

I found a lot of posts that cover macOS behaving strangely with the Realtek 8153 chip:

• Custom driver on Github
• Other Communities Thread covering this
• Old Realtek driver, last updated in 2020

If this were strictly a driver issue, I would assume the Aukey adapter would have the same issue since it is using the same driver. Everything is going through that same single USB-C connector to the MacBook Pro, all I've done is created a nightmare daisy chain to get fast wired internet.

Does anyone have ideas? I've already bought a smaller USB ethernet-only adapter to plug into the back of the monitor, but I hate leaving a mystery unsolved :).