CalDigit TS3Plus Thunderbolt Dock ethernet to FritzBox 7590 is only 100mbit after reboot on Ventura 13.1

Hey you clever folks,

I've got a MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports) running Ventura 13.1 connected to a CalDigit TS3Plus Dock, which connects via a 4 meter cat6e cable to a FritzBox 7590.

After a reboot, the ethernet connection auto-configures itself as 100mbit. If I disconnect and reconnect the ethernet cable, it correctly configures as gigabit.

If I visit Settings/Network/Thunderbolt Ethernet Slot 0/Details/Hardware and change it to Manual configuration at 1000baseT... the connection is disconnected and reconnected, and testing shows it's *still* connected at 100mbit. It stays 100mbit after reboot as well. (Edit: Weird additional detail - if, after physically reconnecting the cable and verifying that it's working at gigabit speeds, I switch to Manual configuration and explicitly set it to 1000baseT, it reconnects... at 100mbit. Same thing if I switch back from Manual to Automatic - forced down to 100mbit again. So, so broken.)

I've verified the FritzBox 7590 is configured for "Power" (gigabit) on all 4 LAN ports.

Rebooting into a Windows 10 BootCamp partition, the connection correctly configures as gigabit.

I believe this started happening with the upgrade to macos Ventura, but I didn't notice the problem immediately, and then blamed it on the old ethernet cable which I've since replaced.

There is an existing question that's very similar from about a year ago: Only 100mbit Ethernet speed with an OWC T… - Apple Community BUT I didn't have a problem until more recently.

Any guesses? My workaround is to plug into a gigabit hub rather than the FritzBox directly. That setup has no issues.