### 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)

uint32_t region_index = p_index / MULTIMESH_DIRTY_REGION_SIZE;
#ifdef DEBUG_ENABLED
	uint32_t data_cache_dirty_region_count = (multimesh->instances - 1) / MULTIMESH_DIRTY_REGION_SIZE + 1;
	ERR_FAIL_UNSIGNED_INDEX(region_index, data_cache_dirty_region_count); 
#endif
	if (!multimesh->data_cache_dirty_regions[region_index]) {
		multimesh->data_cache_dirty_regions[region_index] = true;
		multimesh->data_cache_used_dirty_regions++;
	}
	if (p_aabb) {
		multimesh->aabb_dirty = true;
	}
	if (!multimesh->dirty) {
		multimesh->dirty_list = multimesh_dirty_list;
		multimesh_dirty_list = multimesh;
		multimesh->dirty = true;
	}
}
void MeshStorage::_multimesh_mark_all_dirty(MultiMesh *multimesh, bool p_data, bool p_aabb) {