Slack notifications sent to wrong channel

Summary

Slack notifications are not sent to the correct channel, changed channel in which they should go.

Steps to reproduce

1. Configured everything to go to #project channel. Tested, worked.
2. Created new channel #project-squad and tried to change it in the integration on slack, as well as override them in gitlab, without success, messages go to #project still.
3. Deleted and removed the entire integration in gitlab and slack
4. Created new hook, newly configured the project, still sends messages to #project instead of #project-squad

What is the current bug behavior?

Messages are sent to the old #project channel that was previously configured.

What is the expected correct behavior?

Messages get sent to the new #project-squad channel created

Output of checks

Installation is not maintained by us, so all I see is this from the admin interface: GitLab 8.16.6 GitLab Shell 4.1.1 GitLab Workhorse v1.3.0 GitLab API v3 Git 2.10.2 Ruby 2.3.3p222 Rails 4.2.7.1 PostgreSQL 9.6.1

Notes

We have another project that works just fine that also has a - in the name, like #anotherproject-api and that works fine, though we didn't move that ever.