when it runs the readiness check they all pass but "Cron script readiness check failed"
How to diagnose the «Cron script readiness check failed» failure during a Magento 2 upgrade? https://mage2.pro/t/541
Bug: Magento 2 checks the «.update_cronjob_status» file but never generates it so the «Cron script readiness check» will always fail on a Magento 2 upgrade (and my fix) https://mage2.pro/t/1125