DDM iOS Software Updates over cellular stuck on "Update requested..."

I'm using Declarative Software Update policies deployed by MDM to update our iOS 17.x.x iPhones and iPads to the latest iOS 17.

We have devices that never connect to Wi-Fi, and can only be updated over 5G.

I'm observing that the pending iOS update only downloads over Wi-Fi.

This is even after setting Data Mode "Allow More Data on 5G".

This results in 5G-only devices out in the field never updating, and becoming overdue.

Connecting an overdue device to Wi-Fi immediately triggers the download. Disconnecting again pauses it.

In this example, I'm trying to update a 5G-only device from iOS 17.0.3 to iOS 17.4.1.

Our mobile carrier (Telstra in Australia) doesn't impose any data restrictions on us.

I've stripped off almost every other config pushed by our MDM, and conducted a Network Settings reset.

Any advice on how to permit the full download & install over 5G gratefully received!