VoLTE is working in preinstalled Cyanogen OS but not in CyanogenMod

I was trying to use VoLTE in my phone but eventually landed up with result: 1. CyanogenOS can run VoLTE based SIM card 2. CyanogenMod can't run them. Tried 1. Setting LTE Only option in *#*#4636#*#* 2. Setting APN in Sim Settings 3. Also kept the VoLTE in SIM Slot 1 But nothing worked in CyanogenMod. Does any one have idea how to use both VoLTE and CyanogenMOD both? Currently my phone's CyanogenOS is allowing me to keep only one at a time :) But I want to use cyanogenMod as it is marshmallow and nightly build updates are released.