If you are using headphones with an adapter to go from the 1/4" (6.5mm) size to 1/8" (3.5mm) size, make sure you are using the one that came with the headphones so that it fits properly.
For adapters that did not come with the headphones and so do not fit properly, or are not fully screwed or inserted onto the headphones plug, it could cause some signal from the "positive" contact on the headphone jack to bleed into the "negative" contact. And because these two channels have opposite polarity, this bleed cancels out audio signals that are common between them.
In other words, a stereo audio file that has things panned to "center" so it is present equally in both left and right channels, that sound will end up being cancelled or reduced in volume so it is not heard.
But things that are panned just to the Left channel only so it's not present in the other channel (or vice versa) will be heard.
Most vocals and bass or lead instruments are usually mixed in the center. Where reverb, background vocals, other instruments and effects are panned more to the left or right channels. So when this "center cancel" effect happens, you only hear those effects or background things which often sound "distant".
Check your headphones adapter to make sure it's on all the way (some of these screw into place). Or try another adapter that may better fit the tolerances of the plug on your headphones.