[SOLVED] Vertex shader problem with quads/planes

Hi!

I've been only messing with shaders for two days , so it's entirely possible that i'm missing something really obvious.
So i just basically tried to make a waving grass vertex shader.

 v.vertex.x = v.vertex.x + v.vertex.y * sin(_Time.y);

This is all i wrote before the UnityObjectToCLipPos thing, but i get really weird and inconsistent results on planes and quads. In some cases it works how i would expect it to, and sometimes not. It seems to depend on where i view it from. It seems to work fine with cubes though. I've been modifying a two sided shader i got from the asset store, but the same thing happens with the standard unity unlit shader. (the one you create by rightclick-->create-->shaders-->unlitshader)
Here is a gif demonstrating it(The white quads are just a material with the same shader, but no texture for testing).
As i zoom in and back out the behaviour of the grass blades changes. Also i turned on the wireframe. It seems like the wireframe always behaves correctly, even when the texture itself starts moving wildly. Also when i change one of the mesh filters to cube, suddenly two other quads fix themselves magically. This is so weird that i can't even begin to reason about it.

edit: I'm using 2019.2.2f1, but tried upgrading to 2.6 and it was the same
edit2: While im not using the unity quad mesh, even if i change to unity's quad, the problem persists

 

Interesting and you seem to be very close.

I've found this while trying to understand what you are doing, i still dont understand
the problem because i see like 4 problems at the same time.

https://www.reddit.com/r/Unity3D/comments/6re9e5/using_vertex_animation_shaders_to_make_grass_and/

What happens if you put just one quad with the shader?

 

Okay weird. I tried it in a whole new project with quads and it works consistently there. Once i get home ill make additional tests, to see what the difference is.

Edit: Okay so i cant recreate this in a new project for some reason, but in my main project i did this:
1.Created new unlit shader and a material for it
2. added this line v.vertex.x = v.vertex.x + v.vertex.y * sin(_Time.y) to the shader
3. created a new scene
4.spawned a quad with the material(shader) It worked fine
5. I spawned another one, then it started moving in a unexpected way again.
It kind of seems like it happens when theres more than one, but i have no idea why it doesnt happen in the other project.
Just to clarify, the movement i expect is the one where it just stretches, but doesn't actually move.
I just really dont understand why spawning another one for example changes the behavior.
https://hatebin.com/pyvbiwaqsr Heres the shader, but there's really just one line changed.

 

Okay i finally fixed the problem i think. I had to add "DisableBatching"="True" tag.