If you have upgraded SuiteCRM, it is possible that you may get lots of Undefined labels after the upgrade. This is not an issue with installation or upgrade. It is just a configuration issue.
This leads to an issue with .htaccess for Linux server and web.config for Windows server. It is possible that you have wrong RewriteBase which is causing an issue.
For me, in /config_override.php file, I had explicitly defined site_url which was used to generate RewriteBase. This was wrong when I moved the site.
$sugar_config['site_url'] = 'https://someurl.com/suitecrm_path/';
Once I fixed site_url with correct url and rebuilt htaccess file, all labels showed up correctly.