https://wccftech.com/oneplus-devices-are-experiencing-a-bug-that-swaps-audio-channels/

OnePlus devices are great in almost every aspect; they are the perfect combination of great hardware meeting great software. However, based on a few reports from users around the world, there is a rather strange bug that is plaguing their devices that ends up swapping left and right audio channels when you are using wired earphones. As far as the reports are concerned, this issue seems to be most prominent on OnePlus 7. However, there have been reports on older OnePlus devices, as well.

The first time someone talked about this bug was back in 2014, and while it did seem like an isolated issue. It has popped up a number of times on the forums around the internet.