I HAD this issue as well. I used rubbing alcohol and Q-Tip to clean the metal cage of the bud. I used the Find My Buds to see if it can clear any object that might be blocking the sounds from the inside. I went down to have it looked at but decided against it as they were gonna charge me SGD$122++ (USD$90++) for labor and repairs.
Decided to use a penknife and slowly pry open the metal cage. It was pretty easy to remove after the glue that was used at the factory was softened by the rubbing alcohol. Inside it was a black mesh cloth like material. I suspect it was to prevent even tiner particles from entering the bud. Cleaned it well with the alcohol and Q-Tip. Tested before assembling it back and it was back to normal equal volume. Saved myself some moolah. And Samsung Service Centre SG, if you are reading this, hope you get some coals for Christmas.
The Youtube video below gives an idea how to do it. I would recommend that the black mesh cloth like material be cleaned and placed back.