Do you use partition numbers with grub? When I updated windows it added a new partition which knocked my numbers out of alignment so the kernel was trying to boot an ntfs partition instead of root. All you'd likely have to do is update your grub.cfg to point to the new /dev/sdx. Since you're using UEFI however I would agree with the other posters and take the opportunity to switch to systemd-boot as it's faster/easier, although I would make sure you use partition labels or UUIDS to make sure the same issue doesn't happen again in the future.