I think it’s never going to be possible to determine exactly what the cause of every single issue is/was, given the huge number of variables especially on Windows systems, and the wide variety of hardware combinations. That’s something that applies to all software, not just Cubase. It would be nice to insist on reinstalling both OS and Cubase before investigating, but nobody wants to have to do that.
In critical environments such as hospitals, industrial automation etc., absolutely nothing gets changed without thorough testing on seperate identical test systems, whereas many of us tend regularly to install/uninstall plugins, trial software and whatever else we find on the cover of a magazine, and of course that affects stability. Another common complaint appears to be associated with gamer BIOS and graphics card tweaks, and many mainboard manufacturers’ tweak utilities, as many find it unreasonable to make a massive investment in hardware and then only use it for Cubase. For Cubase I would recommend no overclocking (even forgetting the “K” CPUs and save money) and install nothing except Windows and then check device manager for missing drivers and install them manually – so the bare minimum, in other words.
I built a custom PC around 2007 with what were then cutting-edge components with the intention of running only Cubase 5, but it was a nightmare. On the same machine, without any change to the hardware whatsoever, Cubase 6 ran flawlessly, and even Cubase 7 (and I’m sure Cubase 8, had I kept it that long!), so Steinberg are not blameless either.
These days, other than regular image backups of the OS drive (I use Terabyte Unlimited’s Image for DOS) I just use CCleaner every few months. Overall I find Windows 10 very good and stable, with no issues (at least, none that affect my workflow) on Cubase pro 8.5.15 currently.