The run cadence reported on the website's reporting section does not match the cadence reported on the activity detail page.
In the activity detail for a particular activity I see "Avg Run Cadence: 153 spm". When using the reporting options to select just that activity with a custom date range I see a reported "Avg Run Cadence: 76 spm". So it looks like one of them is off by a factor of two.
It's easy for a user to recognize this error and correct for it, but it also shouldn't be difficult to fix.