Newbie - Lighting has harsh lines on seams

I’m new to UE4, so hi! I realize this is probably a silly question and has been asked a million times but I don’t know what to search for… why is there these crazy seems in my scene? I don’t need my hand held and I’m totally cool with reading documentation, I just need some guidance on where to head.

I just took a plane in UE4 and applied a tileable material to it and set the lighting quality to production.

its literally the first thing in google