How to get rid of terrain light seams?

Greetings everybody!

I have a problem that I can’t seem to solve.
I have a terrain that has these light seams everywhere on it, which I am trying to get rid of.(see picture)
I am using Unity 2018.2.5f1 Personal. The screenshot is from the scene view in the editor. If there is any other information I can provide, please let me know.

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If someone could provide me with some suggestions for a solution, I’d be extremely thankful.
Thank you in advance!

Kind regards,
Alex

Edit: I smoothed out the terrain and the issue seems to only appear where the lanterns light up the area. If I move the lights around, the seams/artifacts are appearing around them but go away where there are no lights.

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bumping my thread out of desperation