Cryogenic Engines mod adds LqdMethane + Oxidizer engines. There is currently no LFO Mixture resource defined with InterstellarFuelSwitch of MethaOxi for these engines, only LqdMethane + LqdOxygen is defined.

Were you able to find a patch for this anywhere?

Ok, I will add MethaOxi in a 3: 1 ratio, just like in Cryo Engines, both to IFS and KSPIE

It is implemented