Shutdown Causes Reboot on TrueNAS Core 13.0-U1

My backup server is running TrueNAS Core 13.0-U1, and when I try to shut down the server using the Web UI and/or console, the server reboots 5 - 10 seconds after it powers off. The server specs are as follows:

Intel R2000 Server with S2600GZ motherboard
2 x E5-2630L v2
32GB ECC RAM
LSI HBA

I've installed the latest BIOS, BMC firmware, Intel ME firmware, and HBA firmware. I've also tried removing all PCIe devices, disconnecting all network cables, reseting the BIOS/BMC to factory...

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