It could very well be a bug, but what kind of ram are you working with?
does it meet the minimum requirements of unreal?
Also we still need any info helpful to reproduce. Size (number of frames) on animations, number of animations.
To put It in perspective for you, I have no trouble importing an FBX with 150 animations of an average of 24frames each.
it takes some time, but goes fine. My system has 64gb of ram though so you know, if I went down to 8, it may not be so fine…