### Godot version

v4.0.beta14.official [28a24639c]

### System information

Windows 10, OpenGL

### Issue description

Vulkan and Mobile:
![Godot_v4 0-beta14_win64_kEcRNiMfNJ](https://user-images.githubusercontent.com/7782218/213967627-8e8755d9-2fe2-43b3-b197-f9f2840b7580.gif)

OpenGL:
![Godot_v4 0-beta14_win64_MQ233TZuPq](https://user-images.githubusercontent.com/7782218/213967651-ae463a6f-c867-4312-bdf1-525e1d7def01.gif)

At first I thought it was related to `set_buffer()`, but it turned out that `set_instance_*` also work incorrectly.
Probably the custom information is also set incorrectly, but I haven't checked it yet.

### Steps to reproduce

* Open MRP
* In the editor, select `MeshInstance3D` node and change the `Count` property
* -- or --
* Start the project and move the slider

You can also switch the renderer to Vulkan and compare.

### Minimal reproduction project

[set_buffer().zip](https://github.com/godotengine/godot/files/10476834/set_buffer.zip)

MultiMesh *multimesh = multimesh_owner.get_or_null(p_multimesh);
	ERR_FAIL_COND(!multimesh);
	ERR_FAIL_INDEX(p_index, multimesh->instances);
	ERR_FAIL_COND(!multimesh->uses_custom_data);
	_multimesh_make_local(multimesh);
	{
		float *w = multimesh->data_cache.ptrw();
		float *dataptr = w + p_index * multimesh->stride_cache + multimesh->custom_data_offset_cache;
		uint16_t val[4] = { Math::make_half_float(p_color.r), Math::make_half_float(p_color.g), Math::make_half_float(p_color.b), Math::make_half_float(p_color.a) };
		memcpy(dataptr, val, 2 * 4);
	}
	_multimesh_mark_dirty(multimesh, p_index, false);
}
RID MeshStorage::multimesh_get_mesh(RID p_multimesh) const {
	MultiMesh *multimesh = multimesh_owner.get_or_null(p_multimesh);
	ERR_FAIL_COND_V(!multimesh, RID());
	return multimesh->mesh;
}
AABB MeshStorage::multimesh_get_aabb(RID p_multimesh) const {
	MultiMesh *multimesh = multimesh_owner.get_or_null(p_multimesh);
	ERR_FAIL_COND_V(!multimesh, AABB());
	if (multimesh->aabb_dirty) {
		const_cast<MeshStorage *>(this)->_update_dirty_multimeshes();
	}
	return multimesh->aabb;
}
Transform3D MeshStorage::multimesh_instance_get_transform(RID p_multimesh, int p_index) const {