Obviously this is 3 years after this thread was started so I expect a lot of things have changed with the engine since then, but either way I just wanted to post this as a reminder for myself:
My solution is to go in the Normal texture itself > Compression Settings > select Normalmap (DXT5, BC5 on DX11). You’ll see the color visibly changing due to the new compression and connecting it to the Material now fixes all the seam issues.
Hope this helps/