Optiplex Micro Plus 7020 and AOC 24P2 monitor not working using DP cable

Hey Everyone,

I have an unusual issue with 3 new Optiplex 7020 that I purchased.

When I connect AOC 24P2 monitors with a DP cable nothing displays. The monitor does not detect an input.

1. I have tried all 3 computers, and I have tried 4 different AOC 24P2 monitors.
2. I have changed DP cables.
3. I have ran windows updates for drivers, no updates were pending.
4. I've used Support Assist on the dell website and the machines are up to date.
5. I have manually installed the driver for the monitor using Device Manager.
6. There is probably one or two things I have forgotten.

What does work?

1. Using a different model of monitor, even AOC.
2. Using the 24P2 monitor with a VGA adapter.

From my troubleshooting it seems to be specific to this model Optiplex, this model monitor, while using DP cable.

Anyone any ideas on how I can solve it without using a workaround like a VGA adapter.

Thanks.