Enable port without Lan-cable

Good day. I have two rb951s on which they mistakenly installed a ROS version lower than it was originally preinstalled. Since then, on any ROS version, the following problem appears: on an empty configuration after power-on, port 5 and port 5 indicator are turned on, the logs display

ether5 link up speed 100m Full duplex

Lan cable is not connected. Deleting the config, updating, downgrading and upgrading by netinstall - nothing helps. POE is disabled. The LED is still on.
A question for connoisseurs: where to look?