I recently developed an issue with my Mac Pro 6,1 and I'm wondering if anyone else has experienced a similar problem. I'm currently on MacOS 10.13.4. If I cold boot the machine and allow it to sit at the login screen, it shuts down instead of going to sleep. Now if I login and then allow it to go to sleep, or manually put it to sleep, it goes to sleep normally. It also wakes up normally. Otherwise, everything else seems to be working as usual. I've tried resetting the SMC and PRAM but this has not fixed the issue. I have also run the Apple Hardware Test without errors. Any ideas?