Title says it really.
Lighting quality is set to production.
Light map coordinate index is set to 1.
Light map resolution is on 256 right now, but has been up to 1024 with no improvement.
This is the result:
Before build (not bad):
After build (ugh):
You have to increase the lightmap resolution of your landscape -> e.g around 4-6 
(the pic is in a pretty low quality, cant see if you have already done that)
Oh, wow! That must be it! I haven’t tested it, but I didn’t edit any of the terrain settings so that is probably the problem. I kept trying to change the wall’s settings because it was casting the shadow it would’ve taken me forever to think that it was the terrain. You saved me a lot of time, thanks!
Yep, that will be the solution, because you always have to increase the lightmap resolution of the mesh/object that should receive the shadow
But be careful with the landscape lightmap resolution, because when you get too high, it will take pretty long to build the light
