Solution Demystified
Ok, so I spent the whole day making this work, and once I struck gold I worked back all of the core settings through deduction and creating many, many, combinations of settings. Here is the minimum set of changes.
version: UE 5.5
hardware: Elgato CamLink Pro - 4 HDMI input Internal Capture Card
- Create a blank live production project.
- Goto Project Settings and change:
- Directx to 11
- Hardware Video Decoding to off (unchecked)
- Goto Plugins and DISABLE:
- Apple ProRes Media
- HAP Media
You will have some restarts requested, but you can make all the changes then just restart once.
You can then create a MediaPlayer and set the source to your Elgato input feed.
Good Luck! (This stuff needs some real AI 
)