Why bones in PhAT push each other away (like a spring)?

Hello everyone,

I’m currently working on a foliage system and I wanted the player to interact with some of them i.e. to bend the plant on collision with player. But putting that aside, I’ve stuck on settin the physics asset for my wheat. It’s made just from a plane that should bend in three places. I’ve rigged it simply in Blender with three bones. Importing to UE went fine (I think) but problems start with Physics Asset.
As you can see on screens when simulation is on, bones start to act like a spring and stretch the model out for unknown reason, even though I set them not to collide with each other (not sure if that’s the way to go?) and set limits on linear movement. What I want to achieve is for the wheat to maintain its original size and be able to bend when a player will stand near it.
Before:

After:

I’ve set the lower bone to Kinematic physics mode (that way it stayd in its place and not fall down), rest are simulated. I’m also posting bodies and constrains settings, hope that helps to get through this.

I would really appreciate any help!
Cheers,
Radek