Github Slackbot is posting to one channel, but not another

[echarrod]

Describe the bug
I have subscribed to various repos with both:

/github subscribe luno/workflow
/github subscribe luno/workflow pulls issues

This worked when I posted to one Slack channel.
But I am doing the same process to a 2nd channel, but nothing is appearing.

Expected behavior

• I would expect to be able to post to multiple channels

Thing I've tried

• Unsubscribing from the working channel
• Unsubscribing and re-subscribing from the broken channel

Screenshots
Debug info:
Working channel

{
  "team_id": "T028ML64H",
  "team_domain": "luno",
  "user_id": "U03S53B3V4Z",
  "channel_id": "C05RR35K1A5",
  "channel_name": "guild-open-source-notify",
  "text": "debug",
  "enterprise_id": "E04MWCRJ9BJ",
  "enterprise_name": "Luno"
}

Not working channel:

{
  "team_id": "T028ML64H",
  "team_domain": "luno",
  "user_id": "U03S53B3V4Z",
  "channel_id": "C04PN76FWQ4",
  "channel_name": "guild-open-source",
  "text": "debug",
  "enterprise_id": "E04MWCRJ9BJ",
  "enterprise_name": "Luno"
}