I have several earbuds that I haven’t used for over a year. When I recently tested them, they all had little volume. After I play them 24 hrs or so, the volume is back to normal. Why is that?
I suggest that you schedule an exorcism ASAP.
But, for real, no idea. Could be the cabling, headphone jack area, or drivers. Also, method of storage can affect longevity and sound quality. People with high-end headphones and earphones take care to not fluctuate between extreme temperatures, keep dust out, coil the cable for correct storage, etc.
I have found that a pair of new headphones/ear buds needs to be broken in by playing it for a few days constantly to get things loose and going.
This could be that process in reverse . . . Maybe. This is just a wild guess, but maybe all the stuff “froze” up and stiffened, so playing them for a while loosened them back up.
I agree with saxmaster on that note. The speaker cones could have gotten a little stuck but playing some tunes could have loosened them