Loopback adapter won't link on M4100-D12G ports

In the process of assisting a relative troubleshoot a new home Internet router, I was recording a video to demonstrate how to test a switch port with a loopback adapter. In the process, I discovered that I couldn't get a linked status on a M4100-D12G switch.

This port provides a connection for other network devices including a laptop and cameras.

I tried both a RJ45 and Gigabit loopback adapter and well as one I'd created myself.

All these loopback adapter work on a Netgear 5-port switch and a home router with integrated switches.

Is there an explaination of this behavior?