U2717D DP Input Signal question

We have some Dell U2717D Displays which are new to us, most of the displays around are the older U2715H.

We're having trouble connecting DisplayPort input sources to them in some cases.

A Dell Desktop PC, such as an Optiplex 3050 with DisplayPort Out, connected to the Monitor with a DP-DP cable - Works.

We've not found anything else that works yet, other devices we want to use but fail are,

A Dell-Wyse Thin Client, which has DP and DVI-I outputs, conected to the DP In port with a Standard DP-DP Cable. No cable is detected.

A Dell Latitude Laptop (5480, 5580,5490, 5590) with a USB-C DP output, connected to the DP-In port using a USB-C to DP Cable - no Cable detected

Both the Laptop and Wyse boxes that fail to work with DP In on the U2717D work fine on the U2715H

(Laptop will work via HDMI to HDMI but this is somewhat limiting if you want to connect two displays)

Is there a fundemental compatibility issue with the newer monitor that wasn't present on the older generation, or is there a setting on the screen I can change? I can't find anything obvious going through the OSD Menu