Hi, I had the same problem with my Galaxy Buds Plus and successfully solved it.
So what causes the problem?
The problem is earwax filling up the grill. Even though you have cleaned the grill from the outside, it can appear clean, but still be quite clogged. The solution is to remove all the earwax.
How to fix it:
1) Take a sewing needle (it needs to be very “sharp” or “pointy”), insert it into any hole of the grill and gently pry out the grill from the earbud.
2) Once the grill is off, you will see the backside of the grill is a black mesh. You will also notice that there is a small ring of adhesive tape falling off the ring around the grill edge.
3) Now you need to push the earwax back out by pressing the black side. For this, use a cotton swab - it helps to distribute the force evenly across the black mesh.
4) When pressing from the black side, you will see some earwax coming out the grill holes. I used a cotton swab and some isopropyl alchohol (any alchohol is fine, I guess…) to scrape it off. Repeat until there is nothing left on the grill.
5) Now, you need to put the grill back on. Unfortunately the grill now won’t stick to the earbud. You need to find a metal/plastic glue and very precisely apply it along the edge and glue them back together. REMEMBER not to use a glue that is too strong as you will probably have to do the whole procedure again in a year and want to be able to remove the grill again.
You’re welcome ;-)