does cable test works on fibre?
https://help.mikrotik.com/docs/display/ROS/Ethernet#Ethernet-DetectCableProblems
Note: Currently cable-test is not supported on Combo ports.
Perhaps worth to note: cable test works (if at all) for UTP copper cables. I’ve yet to see (an ordinary) fibre SFP module that supports cable test (there are specialized ODTR devices which are intended to perform test on fiber).