Here is an interesting problem pointed out to us by an eagle-eared Audio Masterclass student (for preference, you should download this 2 MB .wav file and audition in your DAW)...

mix-problem

It's a mix of bass drum, snare and left/right overheads. Do you hear any problems? Let's listen to the overheads in isolation...

overheads-problem

Listen the the snare drum in the overheads. Does it sound centered in the stereo image, as it should? On a casual listening, there doesn't seem to be a problem. This is probably because of the relatively uncorrelated signals from the kit other than the snare. But when you concentrate your attention on the snare, it is clear that it is...

Out of phase!

Yes, one channel is inverted with respect to the other. This probably happened due to an incorrectly-wired microphone cable. They sometimes come like that bought new and it is always worth checking. The second most likely alternative is that the phase button was down and the engineer didn't notice. So if we invert the right channel (which is the one that is incorrect when compared with the signal from the snare drum mic), we get this in the overheads...

overheads-problem-solved

And with the bass drum and snare...

mix-problem-solved

Problem solved!

P.S. 'Out of phase' is a commonly-used expression to mean that one channel of a stereo pair is inverted with respect to the other. 12 characters versus 66 makes it a useful shorthand.