Having two unity processes is laggy, even when one is paused

I’m developing games for a specialized hardware and I needed to make a launcher for these game on this hardware.

I decided to use unity to be able to use some shaders in the launcher, but more importantly because the controls of the hardware are not usable for navigating in a more standard type of launcher and I must keep them for compatibility with some external games. (eg. Shift, Control).
The launcher stays open in background so it’s accessible when I close the game. (
I launch compatible games which I’m not the developer of, so I can’t just close the launcher and open it back from the games)

The hardware I’m using happens to have 3 screens and I use them all for both the games and the launcher.

On occasions (but often enough that I need to fix it), when I open a game with the launcher using Process.Start(), the game is very laggy.
It doesn’t seem to be a performance issue with the launcher, because it uses nothing in the task manager. Also the framerate feels smooth but with very frequent consistent spikes.

I even used process.WaitforExit() which blocks the thread of the launcher, but nothing changes.

It seems to be a problem with windows managing focus or syncing framerate because opening a program like task manager and going back to the game fixes the issue until I turn the game off and on again.