How to solve undefined labels in suiteCRM

Go to Admin > Repair and do a "Quick Repair & Rebuild". Execute any changes shown at the bottom of the page.

If that doesn't work, go to Admin > Repair and do "Rebuild .htaccess file" and afterward, Admin > Repair and do a "Quick Repair & Rebuild" again.

Simply remove the cache folder from your instance files, and make a hard reload.