If one of these is the case, then you should either turn off or disable the plugin involved prior to the upgrade, and then turn it back on afterwards. If you’re using a proxying cache such as CloudFlare, then it is highly recommended to configure that service to never cache anything in the /wp-admin URLs, to avoid problems such as these.

If you’re not using caches, then a home or 404 redirect is still possible if your browser has certain types of privacy software or extensions running, and if you also have unusual server configurations. The database update screen is also not unexpected in those situations, or if a timeout in the update occurred. If the site is still working after the update but you find any problems, the “Re-install Now” button on the updates screen will overwrite the site files, ensuring that a complete update has taken place. No data will be lost from the Reinstall button.

C.