Each one is a service that passes its tests and still fails in production. Pick one.
When someone exports a report, every other page hangs. The visible tests pass. Work out what production does that the tests do not.
A product page requested while a sales report is being built is answered without waiting for the report to finish.
The report still lists every order exactly once, oldest first, with the same columns, quoting and totals.
Two reports requested at the same time both come out complete and correct.
A report always includes every order placed before it was requested.