Typically the reason is as Melissa pointed out that the zoom level needs to be set at 100% or the red boxes will be offset from the elements.
If your zoom level is set to 100%, then the next thing I'd verify is whether there may actually be two elements for each visible element. If you're using Match Index, change it to 2 and see if it highlights the correct element. If that works, then you might want to consider including a Width>10 or something like that to exclude invisible elements.
If it's neither of those two things, I wanted to ask, does it not work when you attempt to read the Name attribute? I understand that it highlights the wrong part of the page, but it's possible it will still return the right value.
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Dave Morris
3Ci @ Southern Company
Atlanta, GA
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Dave Morris, 3Ci at Southern Company