If you are not using the line fault detection feature in the MAX9275 then you should leave the LMN0 and LMN1 pins floating by disconnecting the pull-up and pull-down resistors.
MAX9275
Production
The MAX9275/MAX9279 are 3.12Gbps Gigabit Multimedia Serial Link (GMSL) serializers with parallel LVCMOS inputs and a CML serial output programmable for...
Datasheet
MAX9275 on Analog.com
If you are not using the line fault detection feature in the MAX9275 then you should leave the LMN0 and LMN1 pins floating by disconnecting the pull-up and pull-down resistors.