Location service only works over wi-fi; doesn't work over USB/Ethernet

[SinisterStairs]

Hello, I just installed Dynamic Dark Mode on my MBP (Mojave), and it continuously errored that my location can't be found / connection timed out. (Yes, Location Services/Automation granted, firewall exception allowed -- keep reading :)

My MBP is connected to Ethernet via a USB 3.0 hub (interface en5). As soon as I unplugged ethernet and turned on wi-fi (en0), DDM behaves as expected and immediately began updating sunrise/set times as I tried different schedules.

If I disable wi-fi and reconnect to ethernet, DDM once again is unable to update my location/schedule. DDM says it will schedule using my previous location rather than erroring, but the sunrise/set schedules don't update as I change them.

I'm running Mojave 10.14.6 on a mid-2015 MBP Retina (11,5).