Hello, good day,
This happened a couple of times. I used MILD to remind myself to remember to do RC in my dream. Then during.my dreams, I did remember to do RC by pinching my nose and trying to breathe through them. I notice I can breathe through the pinched nose but end up not realising that I am dreaming 
You are on the right track.
When doing RC in real life, you need to expect to be in a dream.
You need to insist and even if one RC fail, try another. Really try hard to prove you’re dreaming.
Has happened to me also. As Agent said when you them in real life you need to expect to be dreaming. I would do them half halfheartedly because I know I’m not dreaming for a fact. Now when I do it I think: ‘Can I still breathe?’ ‘What does that mean?’ ‘Why has this told me I’m awake? OK i can’t breathe, in a dream I would be able to.’ Think it through slowly so you do the same in a dream rather than it being a routine non-thinking RC. Same applies to all RCs- think them through in RL even when you ‘KNOW’ you are not dreaming.