One port is up and another port is down, the issue seems to be weird one but it happens when the two switches are connected over fiber. This happens because one side of the switch is not receiving the signal. In the given diagram, see the connectivity of the ports.

The failure of one fiber because of any reason make that port down. The port which is receiving the signal is showing up and the port which is not receiving the signal is showing down. This type of problem leads to the spanning tree loop in the metro ethernet or ring topology. To overcome this problem, UDLD (Uni Direction Link Detection) is required. This protocol forces the both end ports to make down.