Cron and indexers broke right after a Magento upgrade, can you fix that?

Yes, this is common. After setup:upgrade the indexers are marked invalid and need a reindex, new cron groups may need re-installing, and a partial deploy can leave a reindex lock behind. We reset and reindex everything, reinstall the crontab if it was wiped, and rebuild MView triggers that the upgrade dropped. If the upgrade itself is unstable we also look at our Magento upgrade bug fixing path.