I wouldn't be surprised if the entry level Pro machines went Silicone especially. Outside of that one VM instance of
Windows (which may change, depending on what makes it to 11 Pro), nothing that I have is MS or Apple. I guess I should say, nothing that is installed on bare metal is MS or Apple
One thing to keep in mind with running a desktop as a file server is that services that are prioritized for desktop usage, aren't really necessarily for a dedicated server type of application. And the opposite is true as well, services that are for server usage are not prioritized (if even turned on or available) for desktop usage. So there may be some tweaks that could help out in that regard as well.
Was it a store bought, pre configured NAS or was it something that you (or someone else) put it together for this particular application? Sometimes there are bugs in the firmware and the NAS could stand for an upgrade and like some other devices, people don't think about updating them (or sometimes they are worried about what happens when it is updated, given what a NAS is used for more so compared to a desktop), so it may have been something that was fixed and that fix was never applied in your situation. I dunno, maybe y'all did try, I just don't know enough about that situation, just a consideration to have.