Latitude 7450 - External USB-C monitor gets power, but no video/display

Moving from a Latitude 7440 to a Latitude 7450 and running into an issue with the portable USB-C monitor I carry. It's a 2K (2160x1440) monitor and works fine on the 7440, but on the 7450 it gets power, but no display. Plug it into the 7440, works fine. Tried cables that work on the 7440 to check, but does not work on the 7450. I have the latest graphics drivers and BIOS. I tested with a Dell WD19 dock and that works fine. Same result out of either USB-C port. I tried a lower resolution USB-C monitor, and that works fine....so it is something with the 2160x1440 resolution.

Is there something special/different I need to do with the 7450 to get this working? I would expect the graphics on the 7450 to be a little more capable than the 7440! :)