Hi, it seems there is some worldwide issue with Macs right now since Monday night:
A mysterious AVID issue has been affecting computers across the industry.
variety.com
I experienced similar problem today, I noticed Outlook no longer receives emails, Parallels fail to start at all;
after reboot of my hackintosh, it failed to boot at around 60-75% boot strip;
I did High Sierra 10.13.6
reinstall from usb stick (luckily), took roughly 30 minutes;
after successfully booting back into "fixed" OS (all data and software work, nothing got deleted it seems), I noticed "var1" folder in system root, modified today at around 0:56 midnight, which is probably cause of boot corruption (?!), I briefly explored it has something to do with Google and/or Flash...