Occasionally when you add a new member to a private slack channel, Slack will create a brand new channel id and the original connection will be lost, even if you were referencing the channel by name. Slack must still keep the original channel somewhere but not allow it to be accessible.
Because of this, I always reference the channel id for slack rather than the channel name. I get the channel id by opening Slack in the browser and copying it from the url. I store IDs for my channels in a lookup table so that if this happens, it's easy to update the ID in any recipe/process that references that channel.
Interestingly, if you tag users in slack threads, and a user has changed their handle, a similar issue occurs - the ID seems to change in the background so user lookups via slack api don't always give the info you need.
