I upgraded to the High Sierra GM Candidate (from Sierra) a few days ago because I have always had good luck with GMs in the past. Unfortunately, I think this one has issues. After the upgrade completed, it never showed me the "Welcome" to High Sierra wizard and allowed me to login directly (i.e. regular login screen). Right away I knew something wasn't right because the fans came on and stayed on. I gave it a few hours thinking that it's likely Spotlight that's reindexing everything, but that didn't do it. Looking in Console, I saw thousands of log messages with plenty of errors and faults. After some poking, I learned that my iCloud account wasn't signed in so I did that manually, and that reduced the number of errors. The system continues to function, but it's quite unstable, and most of the times it crashes during/right after sleep. Given the above, what are my options? Is there a way to "reinstall" just the operating system files and reinitialize the system without removing all of my applications (and, obviously, losing any data)? I do have Time Machine backups from right before the upgrade and two times after it.