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tsmswifty: have you found out the root cause? I am having exact same behavior.
My Hackintosh (Gigabyte Z390 M GAMING, rev. 1.0, AMD Radeon RX 580) was running smooth for the last 18 month - no problem ever after the first installation of Mojave.
Yesterday my PC started rebooting right after start. I did not install, upgrade or change anything that could explain this behavior. Even more strange, all of a sudden (maybe after 10 reboots) system started working again. (Sometimes I could still work for a couple of seconds before system rebooted and I used this short moments to free some space on boot disk, which was pretty much full.) Yesterday I thought, that freeing disk space was the reason, why the system started working again and it worked perfectly for the rest of the day - even after manual reboots.
But today the system reboots constantly - even quicker than yesterday, so that I can not do anything.
The reboots only happens after I log in with the user. Before user login, the system can show the user login screen without rebooting. Also I found out, that the reboot is much quicker, when the network cable is connected - than it sometimes even reboots before user login screen.
I have Windows installed on the same SSD on a different partition. The system is completely stable when running Windows and I have done all kinds of hardware test, without seeing any issues.
Also, I do not get any hints when reading the spindump of the shutdown_stall_2020-09-02-114900_kermit.shutdownStall
Date/Time: 2020-09-02 11:48:58 +0200
End time: 2020-09-02 11:48:59 +0200
OS Version: Mac OS X 10.14.6 (Build 18G95)
Architecture: x86_64h
Report Version: 28
Data Source: Stackshots
Shared Cache: 0x1dfdc000 4F3AAEE3-7A3A-3917-8D62-4DAEF587F479
Event: shutdown stall
Duration: 1.01s (sampling started after 2 seconds)
Steps: 101 (10ms sampling interval)
Hardware model: iMac18,3
Active cpus: 6
Boot args: dart=0 debug=0x100 slide=0 keepsyms=1 -disablegfxfirmware
Time Awake Since Boot: 61s
Any1 any idea?