Hello, I have the same problem and I would like to be able to contribute to its solution.
Can you tell us more about your setup?
In the functionality configuration I have activated the option keyboard, mouse remote and Touch Screen (absolute). The rest is by default.
what is your viewer type/secondary machine? Android/iOS/Windows?
My type viewer and my secondary machine are windows 10.
Which game are you playing?
I do all this using a laptop and a computer, what happens is that I try to play with my brother from a single computer, but since I only have one monitor I use Spacedesk to be able to play on different screens, he uses a controller on the computer, but When I try to use the laptop keyboard, something similar to "Ghosting" happens in keyboards, it only allows me to press a key when I try to press others, for example, I advance with the "W" and when I want to jump with the "space bar ”Stop moving forward and just jump. This happens both when I use the computer as the main and the laptop as the Viewer and vice versa.
In the following publication I attach the DxDiag files.