On LG G2s that issue was related to app conflict.
Typically, it was related to having OK Google accessible from any screen. Turning that off in Google Now or Google Settings usually fixed that. As of recently, that hasn't been a problem that is widespread since 5.0.2.
Running in Safe Mode (long press power key and long press Power Off and choose Safe Mode) can help distinguish between improper ROM configuration and conflicts with 3rd party apps.
There were some apps that caused issues such as any app that used the microphones like call recording apps, some video calling apps, other phone dialer apps, etc... Keyboard apps that used a mic function for speech to text also contributed to issues.
If you find no issue in Safe Mode than look into apps installed since the problem started. If the issue persists, a factory reset without app and data restore will be necessary.