No clue how often I have landed on this answerhub page: https://answers.unrealengine.com/questions/657159/enabling-recompute-tangent-creates-hard-edges-on-u.html?childToView=932819#answer-932819 I have posted the same solution there.
In your material turn off “Tangent space normal”, then use the “Derive Tangent Basis” function with your normal map and plug the “World Space Normal” output into your materials “Normal” input.
Now, the question is why do I have to do this? From my comparison screenshot, it’s clear that it isn’t a problem related to the seams of the mesh because the tangent base seems to be wrong pretty much everywhere (at the seams it just becomes extra apparent because of the visible line there). Usually, the behavior is that the engine provides you with a correct tangent space for your TexCoord 0 (This is what happens for static meshes and when recompute tangents is turned off). Is there a good reason for this or is this just a bug and ticking tangent space normal should give correct results?