It is often happens that users do not close their articles properly after edit. And others (moderators and admins) cannot edit those articles. There is a special cron task which you can use. It will check in all articles that are checked out for more than 30 minuts.
It makes sense to configure to run command at least once a 30 minuts.
You can use
wget command. For example.
wget http://[site name]/index.php?option=com_cobalt&task=cron.checkIn&secret=123456
[site name] is the root of your Joomla instance and
secret is the secret word you set in Cobalt global configuration.