A short follow-up on my previous post here.
After not using VR for a while and getting many different updates in the meantime (Windows, Nvidia drivers, FlyInside, Steam VR and whatnot) I grabbed my Vive again and tried it FlyInside once more.
Behold, no a crashes! I can't exactly say what happened or why, but it would seem some update - or a combination of many updates - fixed FlyInside. Which is very cool!
It's sad I don't get around to flying a whole lot lately.