I had this same problem with Anker p3i. Extremely low in one ear, tried everything except blu tack! Worked a treat and buds back to normal. Didn’t even pull much wax out but I now have the solution 
Blu tack/white tack is the answer! Thank you to the poster earlier 
Thank you! It worked
just tried the sucking method as both buds were veryyyyy quiet… worked instantly.
Ear wax, dust and /or sticking of the membrane.
Old tricks, we old fellows know,
Great you got them working pefectly again.
here to confirm suck method still a winner
Hello, so I didn’t want to try out the suck method because I think it’s kinda gross lol, so I tried a more extreme version of a clearing water from speakers video and used this for about a minute 31 seconds and my left earbud is almost back to full, if not full volume
obviously don’t play this while it’s in your ear, just hold the ear bud so the speaker is facing the ground and let it run for a bit, i’m sure the longer the better but I only did it for a minute bc im impatient
ive found the fix!!
first, go to settings then accessibility, then go to “hearing” or audio/visiuals
after, turn on mono to have both the headphones with the same audio, and also balance the audio while your there.
if it didnt work its probably earwax, clean it well and have a fun time with your headphones.
lmao. I had the same ideia. just sucked too light. after your comment I did again and it worked. thank you. shame on Anker not having this response in their script.
The “Suck Solution” works! Incredible but really work to me…
Just paired a brand new set of Sleep A20s from the box. Immediately noticed the left bud had almost no volume unless you turned them up all the way. Found this thread before I boxed them up to return. My pair was brand new before I put the buds in, so this wasn’t a wax problem.
I used the “suck” method and then updated my firmware to 01.39. I’m not sure which did it, but they work perfectly well now. Thank you!!!
Suck method did not work!!! As well as cleaning with alcohol and hydrogen peroxyde!!! Got mine just 2 weeks ago
Definitely sucking method is a winner!!! Before buying hydrogen or anything else, try this! Sounds kinda weird but it is effective af
THANK YOU VERY MUCH! This worked perfectly 
Bluetack or white tack as I had handy worked for me. You press it and then pull it out - it goes through the little grid and helped unclog - no visible wax but the sound returned and after about 20 press and pulls the volume was just about as loud on the quiet side as the good side
Thank you so much, I tried everything else but never thought of sucking hard… Now they are back to their best!
I had just experienced the same thing and I FIXED it by going into my audio settings on my device and found the setting that changes which earbud is louder. Just mess about with it till they both the same.
I fixed the problem just try to suck and blow on the lower bud side
I fixed my audio completely. My problem was likely due to a buildup of earwax. What i did was
Wow – so glad I visited here to look for solution. Had tried everything from unpairing to factory resetting and nothing worked. Had extremely low volume from one earbud all of a sudden (possibly following a fall), so I knew it (most probably) wasn’t earwax buildup. Followed the tip here to suck on the grill – AND IT WORKED!!
Probably need to suck hard and several times, ensuring a good vacuum between mouth and earbud.
I have the VR P10’s and I don’t know if this works for every earbud but I used a toothpick and poke a the whole in the middle