The problem seems to conclude that these applications only use the top headphone microphone, that is, it can be used only for noise cancellation. It seems that this problem has also been found in older models, amongst others OnePlus 5, OnePlus 5T and OnePlus 3. Not all apps are damaged; An Instagram, however, does not seem to sound like this when playing OnePlus sound recorded by your device.
OnePlus 6 and OnePlus 6T users are wondering why they're causing the microphone problem when Google Assistant is activated, "Hey Google." To solve this problem, more than one software update is required, even if they are third-party applications.