Hi @Eisen 

Thanks for posting in our business forum.

You looped your switch. That's STP being effective in blocking the ports to avoid a network shutdown.

Select STP (Spanning Tree Protocal) to prevent loops in the network. STP helps block specific ports of the switches to build a loop-free topology and detect topology changes and automatically generate a new loop-free topology.

To effectively fix this problem, you should check the port which is mentioned and see if there is any loop connection in your network topology. Remove the loop and it'll disappear.

When you see this, you are fine. The network should still work. Just warn you that there is a loop and you should take some measures. Or you are using the loop as a backup connection(for this use, refer to the User Guide of the switch)