Why is the number of test executions in the Usage Report different from the number displayed in the Monthly test usage section?
The number of test executions in the Usage Report and the Monthly Test Usage may not match because they display different values:
Monthly Test Usage shows the number of passed/failed tests.
In addition to the number of passed/failed tests,Usage Report includes the number of canceled tests and tests that ended with an internal error.
Also, neither of these values include the number of tests that were executed using "Rerun".
If you want to check the number of billable test executions, please go to [Organization Settings] > [Monthly Test Usage].