I'm not going to talk about VaM particular but more in a general approach.
I've noticed in many cases that the loading speed isn't the only thing but also the streaming of assets. I don't know how VaM is programmed but many 3D rendered software have a special technique build in where assets and textures disappear and appear based on view or position to reduce the stress on your hardware. I forgot the name of this technique.
I'm going to take a simple example, GTA V. The whole map isn't loaded but only 'parts' of it. While you are driving around, assets and textures need to load in. If your HDD is to slow and can't keep up, you will get strange artifacts in screen but also buildings that doesn't spawn in, no roads like you are floating in the air etc. Because the HDD is to slow to stream everything. And everything behind the view of the player despawns to reduce the stress on hardware.
Now this is a weird comparison with VaM but these things can happen aswell in any 3D rendered software, including VaM.
Slower HDD can also cause FPS issue's and framedrops.