How do I stop unwanted zooming in on OS Sierra, Macbook Air 2013 and iMac 2015?

After a few seconds working on various applications, from MS Word, Excel, or Google Chrome Calendar, the app zooms in whether I am using the keyboard, touchpad, or not. This interrupts my work every few seconds and I have to go back to the "View" menu to select "Actual Size" or zoom out to a workable view. Very time consuming and frustrating. This started about a month ago and Apple support by remote call or the Genius Bar have not been able to help me with this. It began happening on both my iMac and my Macbook Air about the same time. I've updated my OS and applications on both devices.