I’ve had this problem for a long time with many animations, so far I didn’t find the reason why it’s happening, but what worked for me was to tick “Preserve Local Transform” when importing animation to UE.
Just today it decided it didn’t want to work anymore 
, so I started searching other solutions and tried changing exporting settings in Blender: in the Transforms tab change Apply Scalings to FBX All - so if the first method doesn’t work, you could try this instead.
If anyone knows better solution/why it’s happening (I always use one rig, sometimes the problem occurs, sometimes it’s totally fine), I’d be very grateful.