Both Airpods pro buds has different versions, one outdated one updated

I have a problem with my Airpods pro that might be uncommon because I haven’t seen a solution for this.

Both of my airbuds are working well, same sound quality when I first bought it. But over time one airbud suddenly didn’t work. I researched and the results I get are the same about firmware update.

Then, I noticed that only ONE airbud is connected to my device, I tried several attempts to connect the other airbud but it didn’t work. Instead, what happened it became 2 separate bluetooth device of the same Airpods pro, literally like:

“Airpods Pro”

and

“Airpods Pro #2”

There I noticed that it has different versions, one has 6A321 (latest ver.) and the other is 6A300 (older ver.)

I know that firmware update works automatically when you plug in your Airpods pro and the device connected to should have sufficient battery, but I did that so many times but I still have the same problem.

Basically, one airbud is updated and the other one is outdated. I can’t use them both at the same time, some features like noise cancellation doesn’t work anymore because it requires two airbuds.

If anyone knows any solution, please let me know. Thank you!