All objects of the car including the window, are children of the main-parent. I've set the street, and the ramp to passive. And the main-parent of the car to active.
The crash consists out of two parts: The animated part, and the simulated part. The crash goes from animated to simulated by animating the checkbox "animated" in the rigid-body-settings to unchecked.
My problem: When I executed the fracture on the window, It would start falling apart right at frame one. Since I wanted it to happen after the crash, I decided it shall go from animated to simulated much later than the main-parent. But once the main-parent goes into the simulated part, while the window is still in the animated, the car goes crazy. Like a glitch, or an extreme epileptic seizure.
I have no idea why it does that. When the window goes into the animated-part at the same time, or even before the main-parent, it's completly fine. I'm out of ideas, of why that happens.
I'm pretty sure it has something to do with the fracture modifer, but there aren't many settings I changed. I've set the shard count to 100, executed the fracture, and animated the checkbbox. That's it.