Smart Slider 3's menu is missing
This problem usually happens, when the system requirement doesn't match, but there could be a wrong installation or server, maybe plugin caused issue as well.
System requirement does not match
Low WordPress version
Error message: Smart Slider 3 requires WordPress version 5.0+. Because you are using an earlier version, the plugin is currently NOT RUNNING.
Solution
Update your WordPress to at least 5.0 to keep your site fast and secure.
Low PHP version
If your PHP version is lower than what Smart Slider needs, you'll see a similar message in your plugin list: Smart Slider 3 requires PHP version 7.0+, plugin is currently NOT RUNNING. Current PHP version: 5.6.2
Solution
Consult your host about upgrading your PHP version as soon as possible, because even PHP 7.0 has reached its end of life and your PHP version is even older than PHP 7.0.
Using an old and unsupported PHP version means it does not receive security updates anymore, so they can put your site at risk. When you choose the next PHP version for your site, you should pick PHP 7.4 ( WordPress' own recommendation) which is a still supported PHP version.
Missing salts
WordPress uses salts to enhance security. If your site doesn't have salts, Smart Slider will not work.
Solution
Make sure the salts are defined in your site's wp-config.php file.
Installation caused problem
Go to WordPress → Plugins and find Smart Slider 3 in your plugin list. Then click on Analyze & Repair which should fix the problem.
Plugin caused problem
A plugin like User Role Editor can limit down where your user has access to. If you have this plugin installed or another user role/capability editing plugin, check its settings and make sure you have the correct access to your admin area!
Server problem
If the previous points won't solve your problem, there will be a server issue. Your PHP files are not able to run either because there is a server cache, which needs to be cleared, or there is a permission issue with your files. You should get in touch with your server host and ask them to help you resolve this problem.