Difference in pageviews or uniques under 10% between IO and GA as well as with other analytics tools is natural.
Here are the most common reasons why the difference can be more significant:
Difference in setup. Endless scroll, galleries, sliders can be tracked differently by different systems.
Tracking codes were not added to all the platforms or the codes were duplicated. By platforms we mean: the mobile website version, AMP, Instant Articles, mobile app.
Comparing different metrics. Make sure you compare pageviews to pageviews, uniques to uniques, etc. Also make sure you select equal timeframes while comparing data.
The average time on page might be not the same, because Google Analytics doesn't count the time spent on the last page in session.
Pageviews numbers per source may differ due to different algorithms - IO dashboard determines the source for page, whereas GA does it for the whole session.
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