y game crashes on/after inject, what should I do?

Update your GPU drivers to latest one, if it doesn't help you can try to switch Graphics API to DirectX12 and set the screen mode to borderless in RDR2 settings.

I caught "fiber exception" when was playing, my menu started not working correctly.

nload menu by pressing button on your keyboard, then re-inject it in game. If that doesn't work, delete the default.json configuration file in the directory where you first ran the launcher. Some functions may cause an error.