I'm using Houdini Engine to create a box, fracture it and also create collision and set "Simulate Physics" to true - all in Houdini and nothing of this is done manually in Unreal.

Interesting: If you disable "Gravity" by hand in Unreal, the Box is NOT falling anymore (like expected). BUT if you enable it again, the Box is STILL not falling. It seems that there's a glitch in the system and then you have to rebuild your HDA asset.

Attribute Documenation: https://www.sidefx.com/docs/unreal/_attributes.html
Collision Documentation: https://www.sidefx.com/docs/unreal/_collisions.html