After updating to Catalina on my late 2013 iMAC Random shutdowns ensued when my Thunderbolt external drives were mounted. Tried various fixes, clean install, fresh backups, many calls to Apple Support… eventually bringing the iMac into my Apple Service Provider, along with the external hard drives I used for backups, both of which were connected via the Thunderbolt 1 interface. They rebuilt (as it were… cleaned up) the iMac Fusion Drive, redid the clean install, and tested both external hard drives, reformatting one of them (at some cost). They could find no hardware issues with the iMac.
Random shutdowns occurred only when Thunderbolt external hard drives were mounted. So replaced with new USB external drives… no more shutdowns. I retired the one WD T-drive and Griffin replaced the G-Drive Pro along with a new Thunderbolt cable under warranty. However, random shutdowns (crashes) persist… only when the G-Drive is mounted, not when the USB external drives are mounted. This is after even a very new clean install, and migrating over only User Data, no Applications or Network settings from the latest TM backup.
I have a feeling Catalina is not playing nice with the Thunderbolt interface (yes, we’ve done all the PRAM and such resets)… hardware? But problem occurred only with Catalina install.
Any opinions are welcome!