A report and a dashboard built from the same widgets can show different numbers, because they usually look at different days.
The report uses its Reference date, counted from the day it was sent. A report sent on the 1st with End of last month shows the last day of the previous month.
The dashboard shows Yesterday by default, or whatever dates you picked.
To compare them, set the dashboard to As of date and pick the date shown as Data as of in the report.
Data can also be corrected after a report goes out. A report always shows the data as it was when it was sent.