Occasionally (every few days or so) when I sleep my iMac, it shuts off while sleeping. It won't wake using keyboard/mouse, and when I push the power button, it cycles through the normal boot-up progress bar. Apps re-launch on login, but unsaved work is lost—for example, Photoshop opens with "Recovered Document XYZ." What's going on?
iMac Line (2012 and Later)
Here's an article from Apple that provides some troubleshooting info that may apply to your situation.
https://support.apple.com/en-us/HT200553
Can you tell us a bit more about your iMac including what model it is, what version of macOS it is running, how much memory it has installed, and whether you've added any memory upgrades.
Here are the steps I would take if it were my system. Most of the steps are listed in the article linked above.
Make sure all of the macOS updates and application updates have been installed.
If you have installed a memory upgrade, consider temporarily removing the memory upgrade and use only the memory that the iMac shipped with to see if the issue goes away. Verify that any memory upgrades meet the Apple specifications, and buy only from a reputable memory vendor to ensure compatibility.
Disconnect all peripherals other than the mouse and keyboard to see if the issue persists.
Create another user account to see if the same issue still occurs.
Here's an article from Apple that provides some troubleshooting info that may apply to your situation.
https://support.apple.com/en-us/HT200553
Can you tell us a bit more about your iMac including what model it is, what version of macOS it is running, how much memory it has installed, and whether you've added any memory upgrades.
Here are the steps I would take if it were my system. Most of the steps are listed in the article linked above.
Make sure all of the macOS updates and application updates have been installed.
If you have installed a memory upgrade, consider temporarily removing the memory upgrade and use only the memory that the iMac shipped with to see if the issue goes away. Verify that any memory upgrades meet the Apple specifications, and buy only from a reputable memory vendor to ensure compatibility.
Disconnect all peripherals other than the mouse and keyboard to see if the issue persists.
Create another user account to see if the same issue still occurs.
I do have a UPS connected via USB, and my Mac occasionally mistakes the UPS's self-test cycle as a running-on-battery event. I have the auto UPS shutdown set to a longer interval, so theoretically it shouldn't be an issue, but I've disconnected it to see if that solves the problem.
Other unusual devices are third party RAM, a WD USB 3.1 SSD, a 21" Apple Studio Display via third party DVI to Thunderbolt 3 adapter, and two hubs. I'll start yanking it all if disconnecting the UPS doesn't do it...
Hardware Overview:
Model Name: iMac
Model Identifier: iMac19,1
Processor Name: Intel Core i5
Processor Speed: 3.7 GHz
Number of Processors: 1
Total Number of Cores: 6
L2 Cache (per Core): 256 KB
L3 Cache: 9 MB
Memory: 16 GB
Boot ROM Version: 220.270.93.0.0
SMC Version (system): 2.46f12
Serial Number (system): D25YX154JV40
Hardware UUID: 156C5900-68DA-5E96-94A9-F05006CF04E8
2019 iMac unexpectedly loses power during sleep
