Sentry Changelog

When your team members take action on Sentry Issues, Sentry will reply to the original Issue Alert message.

If your alert rule notifies a team channel about the same issue, Sentry will reply to the existing Issue Alert Slack message as a thread. This helps you track alerts for that Issue in easily consumable threads

In case you prefer the current behavior you can go to your Organization Settings->Integrations->Slack and disable these changes.