You placed the relief fan onto the main branch, when you should instead add it to the AirLoopHVAC:OutdoorAirSystem:EquipmentList (named West Data Center OA Equipment)

I located one example: Take a look at file 5ZoneAirCooledConvCoef.idf, circa line 2690: https://github.com/NREL/EnergyPlus/blob/f1a13ce86414694ee4f76da536cc08ff19f27fd8/testfiles/5ZoneAirCooledConvCoef.idf#L2686-L2691

AirLoopHVAC:OutdoorAirSystem:EquipmentList,
  OA Sys 1 Equipment,      !- Name
  OutdoorAir:Mixer,        !- Component 1 Object Type
  OA Mixing Box 1,         !- Component 1 Name
  Fan:VariableVolume,      !- Component 2 Object Type
  Relief Fan 1;            !- Component 2 Name

If instead you wanted the fan placed before the AirLoopHVACOutdoorAirSystem (to control the total flow of return from zones), then your node connections just don't match.