Normally you just have to export them as an ordinary fbx file -> when you import it, make sure to enable “import morph targets”
How do you reimport the mesh? -> what happens when you just import it into a new folder?
Could you post some more information about your mesh -> how have you created the rigg, the animations,… + which blender vesion do you use? (the latest one should work fine with the UE4)
Just upload the image on gdrive, dropbox or any similar sites 