Well with an erratic system and only having limited info given to me at this point. Eliminating any possibility of mixed gases seems a good option. Of course looking at my superheat subcool comp amps and performance of system are a prerequisite to my suggestion. I am confused about what you are suggesting. Of course I would diagnose the unit!! Usually when a customer says this may have happened means it definitely did
One would have to at least inquire further how he knows the refrigerant is mixed?