Supportability of MPC10E 3D MRATE-15xQSFPP FPC on MX960.
MPC10E 3D MRATE-15xQSFPP is not supported on slot 1 on a MX960 and you will notice "---Unsupported slot---" in show chassis fpc command output.
show chassis fpc reports as "---Unsupported slot---" if MRATE-15xQSFPP inserted into slot 1 on MX960
This is expected behavior and MRATE-15xQSFPP doesn't support on FPC slot-1
Please refer the public documentation for the further details.
https://www.juniper.net/documentation/us/en/hardware/mx-module-reference/topics/concept/mpc10e-15c-mrate.html