After reading the documentation, I realized that the blend different anims/blendspaces within one sync group preserve only same normalized time position in blended nodes. Play rate matches to leader node without smooth weighted average between all sync group participants. It can cause a sharp play rate changes when another animation becomes the leader.
On video we can se how play rate instantly changed between normal and decceleration animations.
And on second video we can cleary see how play rate changed with very small weight changing between 0.499 and 0.501
Any ideas now make smooth play rate transition within sync group? For example i can put anims in one blendspace (in blendsapces play rate has smooth transition), but i have many many synced anims/blendspaces. I cant put all anims in one blendspace node.