Yea when I export the uasset it allows you to save as .copy or .t3d
when you try and import either of those files it says unknown extension.
It exports the file in text object form, here is a sampling
Begin Object Class=AnimBlueprint Name="Player_Anim_BP2"
Begin Object Class=AnimationGraph Name="AnimGraph"
Begin Object Class=AnimGraphNode_StateMachine Name="AnimGraphNode_StateMachine_1"
Begin Object Class=AnimationStateMachineGraph Name="Movement"
Not sure how relevant this answer will be considering how old this question is, but I had a similar issue. I just closed the project, deleted the binaries folder, and then opened the project again. Fixed the corruption