If you get errors like this when upgrading LibreNMS to 1.40, see the article Resolving LibreNMS error "RuntimeException: The only supported ciphers are AES-128-CBC and AES-256-CBC with the correct key lengths" for a solution.
[root@beast42 /path/to/librenms]# tail -100 logs/librenms.log
[2018-06-04 18:16:17] production.ERROR: RuntimeException: The only supported ciphers are AES-128-CBC and AES-256-CBC with the correct key lengths. in /path/to/librenms/vendor/laravel/framework/src/Illuminate/Encryption/Encrypter.php:43
Stack trace:
#0 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Encryption/EncryptionServiceProvider.php(27): Illuminate\Encryption\Encrypter->__construct('', 'AES-256-CBC')
#1 /path/to/librenms/vendor/laravel/framework/src/Illuminate/Container/Container.php(726): Illuminate\Encryption\EncryptionServiceProvid