I have a fairly high speed internet service (300Mbps). I have another desktop plug to the same dumb switch and using fast.com to confirm my speed is about what I expect. But, when I test the speed with a XPS 9550 + TB16 ethernet connected to the same switch, I'm only getting around 100Mbps even after I've upgraded to the latest Thunderbolt controller driver and ethernet driver.
My audio line out is connected to the back of the TB16 as well. The audio started getting some noise after about 30min use and I had to unplug and replug to get rid of the interference. At the end, I had to just not use the audio after the driver failed to re-recognize the connection. But, alas, without the audio connection to the TB16, my ethernet speed is up to 300Mbps again. Also, audio connected to the front headphone jack also slows down my ethernet speed too.
Hope this resolve someone's quest for full ethernet speed from their TB16.
RE: TB16 ethernet speed affected by audio connection
Have you installed the recently released update for the TB16's ASMedia USB controller driver? There's also an Ethernet FIRMWARE update for it, for what it's worth. The fixes don't list anything about this, but the release notes don't always list all fixes. If neither of those fixes the issue, is this consistently reproducible, i.e. as soon as you connect audio, your bandwidth dips, and as soon as you disconnect, it goes right back up?