Google Chrome	70.0.3505.0 (Official Build) canary (64-bit)
Firmware Version Google_Eve.9584.160.0
No magnification on, display looks like 1200 x 800 (Default), font size Medium (recommended), no zoom (set to 100% for this page in the Chrome menu) 

Steps to repro:
# Create a new presentation in Google Slides
# Create a new slide that has a title and text box beneath it
# Put text into the title field and multiple lines of text in the text box
# Make sure text box is selected (surrounded by a blue highlight)
# Use STS on entire slide using search + draw rectangle around slide
Expected: just text is read
Actual: last line of text is read twice while the pink rect is on the upper corner of the text box

This does not repro on the title text in that slide or if you use mouse selection and then press ctrl + s.

Please see video showing all the ways it does work and then the bug behavior.