Custom Mesh rendering problems

Hello everyone.
I build custom meshes for my 2d game in order to generate a gameworld out of various tiles. These Tile consist of 4 vertices and 2 triangles each. Since i wanted each tile to be able to portray something different through their uv settings the tiles don’t share vertices.
The textures are rendered as “sprites/default” in order to not require lightning.
Now my only problem is that in regular intervales a single line gets rendered between these tiles and i can’t figure out what causes this.
Anyone have an idea, i am gratefull for every sugestion.
Also i apologize in advance if this is a stupid question. I only just started programming games with unity and am not familiar with it.

Here is a screenshot of the problem