Blender to Unreal can sometimes be a nightmare. I’ve made tutorials about it but I handle everything on a case by case basis as I sometimes still get the strangest errors.If you’re willing to share the file I can have a look for you and maybe provide a solution.
Know this sounds like a no-brainer, but check and make sure your entire hierarchy is parented to your root bone (i.e. not having multiple roots). I was having same issue, but unlike most times UE wasn’t spitting errors out at me for some reason. Hope this helps.