Same thing here. It can happen several times an hour. Most times, it recovers after part of a minute, but sometimes it never comes out of it and the only option is to force a shutdown. I have my Mac's clock displaying the seconds count, and even that freezes.





Like others here, I've tried many troubleshooting techniques, i.e. Safe Boot to clear caches, zapping PRAM, running Disk Utility, using 3rd party maintenance and malware-scanning apps (Onyx, MalwareBytes) - no joy.





Was hoping the Supplemental Update would bring relief, but no such luck.





MacBook Pro (Retina, 15-inch, Mid 2015) 2.5 GHz Core i7, 16 GB RAM, original Apple SSD.