This can happen anytime the device only partially boots. So if you’ve had power glitches in general, that can cause it. Or if you were rebooting it somewhat rapidly, that may also cause the failover.
Normally, you can just unplug it, or use the LuCI shutdown method (if available on your device with advanced-reboot) or the cli poweroff command. But don’t use a reboot before you pull power because that will get you into the same situation if power is disconnected during the boot cycle.
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