Usage Metrics Report poor data integrity

Hello all,
I am trying to get data from the dataset 'Usage Metrics Report' in order to store the views we have in our reports.

I would expect that if a user visits 3 pages in a report in a given date I would have three records in the table 'Report page views', and one record in the table 'Report views' for that user, report and date.

Nevertheless, I find some records in 'Report Page Views' without record in 'Report views' and vice-versa. Seems there is no data integrity. The unmatching records reach 10% in some reports, which is a lot.

Anyone can help me to understand why this happens?