### 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)

if (multimesh->buffer) {
		GLES3::Utilities::get_singleton()->buffer_free_data(multimesh->buffer);
		multimesh->buffer = 0;
	}
	if (multimesh->data_cache_dirty_regions) {
		memdelete_arr(multimesh->data_cache_dirty_regions);
		multimesh->data_cache_dirty_regions = nullptr;
		multimesh->data_cache_used_dirty_regions = 0;
	}
	multimesh->instances = p_instances;
	multimesh->xform_format = p_transform_format;
	multimesh->uses_colors = p_use_colors;
	multimesh->color_offset_cache = p_transform_format == RS::MULTIMESH_TRANSFORM_2D ? 8 : 12;
	multimesh->uses_custom_data = p_use_custom_data;
	multimesh->custom_data_offset_cache = multimesh->color_offset_cache + (p_use_colors ? 2 : 0);
	multimesh->stride_cache = multimesh->custom_data_offset_cache + (p_use_custom_data ? 2 : 0);
	multimesh->buffer_set = false;
	multimesh->data_cache = Vector<float>();
	multimesh->aabb = AABB();
	multimesh->aabb_dirty = false;
	multimesh->visible_instances = MIN(multimesh->visible_instances, multimesh->instances);
	if (multimesh->instances) {
		glGenBuffers(1, &multimesh->buffer);
		glBindBuffer(GL_ARRAY_BUFFER, multimesh->buffer);
		GLES3::Utilities::get_singleton()->buffer_allocate_data(GL_ARRAY_BUFFER, multimesh->buffer, multimesh->instances * multimesh->stride_cache * sizeof(float), nullptr, GL_STATIC_DRAW, "MultiMesh buffer");
		glBindBuffer(GL_ARRAY_BUFFER, 0);
	}
	multimesh->dependency.changed_notify(Dependency::DEPENDENCY_CHANGED_MULTIMESH);
}
int MeshStorage::multimesh_get_instance_count(RID p_multimesh) const {