"Unfortunately, Google App has stopped". Locked out of my phone! Please help!
I have a possible solution. But I don't think it works most of the time.

When you are at the lock screen and your keyboard doesn't pop-up, connect the phone to the charger or your laptop/desktop. It resets the processes and your phone will come back to normal. Disconnect the cable if connected previously. After the lock-screen is opened, take a gap of 20 - 30 seconds and connect it and try opening it.

This is an old regulation for many android phones and worked a lot of times in my case with Sony Xperia SP C5302. Hope it works in your case also.