Have you ever had a mix that sounded really great until you turned it down?
My hand is definitely up on this one. It's so tricky! There are actually scientific reasons as to why that is happening when it does.
It's the same situation that occurs in a choir setting. There is always that one person (God love'm) that just can't carry a tune, and so everybody else starts tying to drown them out. The result is a choir that sounds good until they get to that quiet part where all the singers have to bring them notes down a notch. Then all of the sudden the awkward smiles start forming on faces, and everyone starts trying to pinpoint "that guy".
The same thing happens in a mix when we start out mixing to loud. We get it sounding good and then we add that next instrument. Suddenly things aren't sounding quite right so we grab them faders and go to town. Ahhhh, there we go, it's gone! Until that break comes and things start dropping out right before the big swell pre chorus. Then like a thorn in your side it begins to grate against you. Problem is, now you have done so much to mask it earlier that it is hard to find it in the crowd of tracks.
The best way to avoid this that I have found is to simply mix at lower levels. Then not only is my imperfect room performing better but the mix has added clarity. Turn that mix down a bit from the get go and take that mask off the mix.