If you deleted samples files, you may have an error such as :
update-cron.ERROR: Cron readiness check failure! Found non-writable paths:
/magento2/.htaccess.sample
/magento2/.php_cs
/magento2/.travis.yml
/magento2/.user.ini
/magento2/CHANGELOG.md
/magento2/CONTRIBUTING.md
/magento2/COPYING.txt
/magento2/Gruntfile.js.sample
/magento2/ISSUE_TEMPLATE.md
/magento2/LICENSE.txt
/magento2/LICENSE_AFL.txt
/magento2/nginx.conf.sample
/magento2/package.json.sample
/magento2/php.ini.sample
/magento2/pub/.user.ini [] []
it seems that they are necessary in order to not find a massive update.logupdate.log file due to cron checks...
