I believe the first document you site is rather dated, the second one is more current. The latest technical documentation for the MGBLH1 state that it is compatible with SMF, no reference to MMF. Check table 2 of this document for the current specs. If you are trying to use it with MMF that is likely the cause.
Sx550X, Sx350X, Sx250: PSE will Supply Power to Catalyst PSE Ports
May 31, 2016
June 5, 2017
Configure Remote Network Monitoring (RMON) Events Control Settings on a Switch through the Command Line Interface (CLI)
Remote Network Monitoring (RMON) was developed by the Internet Engineering Task Force (IETF) to support...