Windows is usually the side that causes problems, so if you stayed out of it or supervised the updates that could be why. The most common killer combo is that

Windows is usually the side that causes problems, so if you stayed out of it or supervised the updates that could be why. The most common killer combo is that Windows tries an update, reboots as part of it, and the reboot unexpectedly (from Windows point of view) goes into Linux. Some time later you log into Windows, it looks at the clock, realizes the reboot didn't go as planned, and flips its shit into some kind of hare-brained recovery process that winds up overwriting your bootloader with something that can't load Linux and can't load Windows either. It doesn't happen every time so clearly there are heuristics, but it definitely happens some of the time because the dead windows loader it leaves behind is distinctive and unmistakable. That said, I've seen both Ubuntu and Fedora updates that automatically fixed the bootloader until it was broken, so it's wrong to fingerpoint too hard here. The upshot is that "leave bootloader on boot drive alone" isn't part of the implicit operating system social contract, but "leave bootloader on non-boot drive alone" is, so you can solve a big hairy software problem with a small hardware investment.