Greenbone/OpenVAS just hangs when starting or resuming a scan

I'm a very big fan in the open source tools Greenbone Vulnerability Manager and OpenVAS (Open Vulnerability Assessment Scanner). Greenbone is basically the web portal GUI front-end to OpenVAS. Combined, they are excellent tools for discovering vulnerabilities in your network. When it works, it works great! When it doesn't... It's frustrating as hell!

Anyway, the other day I kicked off a quarterly scan of my network, and most of the scans finished, but after a while the server was accidentally rebooted by one of my systems administrators and a number of scans got stuck in a stopped state. When I tried to resume the scan, Greenbone would just spin and nothing would happen! Annoying right?

Well, the issue turns our to be a Redis cache issue. It apparently needs to be flushed when stuff like that happens. To flush that cache run the following from the terminal:

sudo redis-cli -s /var/run/redis/redis.sock FLUSHALL

After running that, I was able to kick my scans off again!