Broken UV
I had an issue of broken UV when I copied a UV map of an object to another object, which in most cases is the duplicated object, with Transfer Attributes. This might have something to do with vertex order of a UV-copied object and a UV-pasted object. If there has been made any kind of change on the destination object, such as applying Mirror function, then the vertex order could have been modified.
Transfer Vertex Order
Troubleshoot this problem with Transfer Vertex Order function.
Click Transfer Vertex Order and do as Maya says.
First, click three closely positioned vertices of the object of which you want to copy the vertex order. Then, click three vertices of the same spot in the same order, now, on the object you are about to paste the vertex order. It’s best to use three vertices that are very closely positioned.
Now, copy and paste the uv of a source object to the destination object with Transfer Attributes. The texture will look successfully applied to the mesh in UE4 as well.
