Certain characters in open sans font appear in the wrong size

I have attached the PDF file. Depending on how far you zoom in, some chararacters appear bigger or smaller than the rest. In the first screenshot you can see that every a and e is too big. And in the second you can see they're slightly too small. This is dependant on the zoom level.

The example was compiled with XeLaTeX and is using Open Sans Regular downloaded from https://fonts.google.com/specimen/Open+Sans. None of the other PDF readers have this issue. Is there something taht can be done to fix it?