I'm using an LG G3 with Marshmallow (Android 6.0, version VS98546A for the G3). The key labeled with a picture of a microphone disappeared from all applications (text messaging, chatting, etc.) supporting speech-to-text capability. This happened on March 4, almost two weeks after Marshmallow was installed and working fine. After speaking with John (a VZW level 2 tech), we concluded that I had done nothing obvious to make this happen. Nevertheless, the real concern was... How do I get it back?
The answer? Select the following:
Settings
Language & Input
LG Keyboard (Under Default)
SELECT MORE (Under Change keyboard)
Automatic (Under Google voice typing)
A master (i.e. hard) reset will probably do the job too, but this solution takes 10 seconds.