I found taht it's possible to open few vmix windows at a time. But if you start external outputs on both windows FMLE goes crazy and don't show correct image.

I would sudgest that if few vMix windows is opened it would be configured that in FMLE you could choose eather vMix Video1 for firs window eather vMix Video2 for second window.
It would be useful if you have few dublicated video inputs (from decklink duo) and need to stream one input with one graphics other one without any or with different graphics (put other logo). As well if need to put gain on audio source (what FMLE don't have.)

Hope you understood my thoughts:)