Animation Montage not playing correctly

So I have edited an animation sequence and simply created an animation montage from it. But it is not the same as sequence. There are parts missing from animation.

so I have this knife idle animation. I just ritated Upperarm_r and lowerarm_r so it looks like I am stabbing. Skeleton is UE4mannequin. and thats it . When i create a montage from that knifeidle animation everything is good but when I rotate the bones and create montage the montage is not playing anything. just standing in pose. and when I double click on the animation that is in montage it looks normally.

go more into detail, is the start time and end time different from the length of the animation? did you change the start position? are there more than one animation in it? did you edit the blendin/out time? theres a bunch of things that could effect this