Hi there Quick questions: -what cassette ratio are you running? -are you running the longer cage derailleur? (To be used with 51t cassette) If you have a GS instead of a SGS it might be the issue. *Also, check that your shifter is set to 12speed, the shifter can be set to work on 11spd systems. (Bottom of the shifter there is a tiny screw) See pic attached From the web: Shimano has three new rear derailleurs to accompany these four drivetrain configurations. The long-cage RD-M9100-SGS is compatible with both 10-51t and 10-45t 12-speed cassettes. The short-cage RD-M9100-GS is the go-to gear changer for riders dedicated to running 1x drivetrains with either 11- or 12-speed 10-45t cassettes.
