Please clarify with the following information:
1. What Magento 2 version do you use? Check your version in the cli with the next command:
php bin/magento --version
2. How do you determine, that you cannot save product data? Do you get any errors or exceptions? Please check files under the /var/log folder.
3. If it is your development environment, then change your magento installation to the developer mode with the next command:
php bin/magento deploy:mode:set developer
4. If you get any 500 errors, then in the file
(magento installation)/app/bootstrap.php uncomment line 11. Change
#ini_set('display_errors', 1);
to
ini_set('display_errors', 1);
But do it only if it is NOT you production environment but only developer. If you don't have developer environment of your website, then create the copy of your website, which nobody access but only you, it will be useful, as you will be able to test all your new changes and customizations there.