I have the iPhone 6c and have up-to-date 9.3.1 software. When I ask google a question on the microphone the response volume is very low. The volume on google maps, all music apps, Siri,etc , very thing but the before mentioned Google volume problem is fine. My Bluetooth is off . I also tried deleting Google app and reloading. After reloading Google the 1st attempt at a mic question the volume works great. Second attempt I am right back to the low volume. It's frustrating, please help.
All I can really contribute this to is that Google designed their apps to work on Android, which uses separate volume sliders for Ringtone, Notification, Touch Feedback and System Sounds, and Music, media, etc....
I would think that Google app for iOS would be designed similarly, but I cannot swear to that.
I have not seen any app volume problems since the upgrade. I take it when you turn the volume up it is at max. If you have headphones on is it the same problem or is it load. Also reboot the phone again if you have not done that.
2 places I know that could affect volume - worth a try:
1) Settings/Music, scroll down to playback and make sure volume limit is off, also turn of equalizer if it is on to see if that is doing anything. Also turn off sound check as a test if it is on.
2) Settings/Maps - Change Navigation Voice Volume from Normal volume to low volume or no voice as a test.