It is always misconfiguration because duplex mode is a L1 configuration issue. If there are L1 issues despite matching DM and a flawless cable, at least one NIC is broken. I suggest you consider two facts about auto-configuration: Neither does every device support auto-configuration, nor is there certainty that both interfaces will running in full-duplex mode.
Considering power outage, that would be a cause of misconfiguration. The interfaces would have to negotiate once again. Either the manufacturer properly documents its devices or you can only guess how the NIC prioritizes duplex and data rate.
Gigabit Ethernet mandates full duplex operation, yet still allows half-duplex. However, duplex mode is a factor whenever Fast Ethernet or less are available. There are still devices in use which do not need more than 100 Mbps because it links to a line which will never deliver more speed.
Then there are devices without a Web interface or CLI. These use tiny DIP switches for HD and FD. A method which probably causes confusion among users.
And there are devices by the same manufacturer which are out of line with the rest of the series. For example, all devices mandate AN, except for one device. Maybe no one would expect that. So to say - never dismiss misconfiguration.