Alerts to Slack

I have a Chronograf setup with TICK and alerts set up to Slack.
For some reason every alert results in two identical messages being received by Slack.
There is only one associated event in the Chronograf log.
If I send the test message I only get one.
Anyone come across this before and how do I correct it?

Do you have multiple subscriptions configured?

SHOW SUBSCRIPTIONS from InfluxDB shell: