Hello,
If you journal fills up that means something was wrong with your graylog instance. You may have other issues, to many to list here.
Best bet is to dig through you Logs files for Graylog and Elasticsearch. Perhaps some curl command to find out if elasticsearch is functioning correctly . If so, then I would restart Graylog service and Tail its log file /var/log/graylog-server try to find out anything on what’s going on.
Not much I can do here to help. You need to show more information.