I got a bit trouble understanding the problem/setup =)
(1) you play a particle system in the montage and that particle system does play correctly when you play the montage?
(2) does the montage have root motion?
(3) if (2), then did you enable root motion from montages in the animation blueprint (should be the default setting)?
Otherwise I have no idea, but can only suggest that you try to pin it down by first only playing the montage without anything else going on, and then step by step reenable all the logic until you have what you currently have and see where it fails.