The common form of this bug is way older than 10 years and isn't really specific to macOS.
The problem is that audio devices do not have an explicit concept of "balance". It's set by adjusting the level of each channel. That volume adjusting process is not reliable. It often happens over an unreliable interface where some volume adjustments are just dropped. This hits a second problem: the audio device often has the ability to adjust its levels out of band with the host audio stack. Thus your laptop has to periodically poll the device to find out what the current actual audio levels are. When your laptop sees that the volume per channel is not equal, it doesn't know if this was caused by the device itself adjusting the balance or the volume adjustment message being ignored.
So for example:
1. User tells laptop to increase volume from 50% to 60%
2. Laptop tells device's right channel to go to 60% (success)
3. Laptop tells device's left channel to go to 60% (failure)
4. Laptop checks with audio device, sees 60% on right and 50% on left
5. Laptop changes audio balance to be nudged to the right
There are some ways to mitigate the problem. The audio stack could try to detect when its level commands are being dropped, but that risks the audio stack and device "fighting" over the correct volume. Better closer-to-realtime scheduling can reduce the risk of messages being dropped.