I've been trying to fix this for quite some time now. All the solutions I find seem to be for sprite sheets. I am using tiles I downloaded from the asset store. They are not sliced up by unity but rather single pngs already separated in the asset folder.
When I combine them to platforms I sometimes get lines between the tiles where the background shows through. These lines are only visible while moving over the tiles. I couldn't manage to screenshot it as of yet.
I have tried creating a material with Pixel snap on and assign it to my prefab but that didn't work. Even assigning the material to all the pieces of the prefab didn't work. The lines usually only show in between prefabs anyway.
Thank you very much!