2026-01-08: Highly flakey smoke tests for batch comments caused by ActionCable feature flag

Highly flakey smoke tests for batch comments caused by ActionCable feature flag (Severity 3)

Problem: The smoke test 'Create Batch comments in merge request user submits a non-diff review' is intermittently failing in staging canary, with initial intermittent passes after a recent rolling restart.

Impact: Smoke test for batch comments in merge requests is highly flakey in staging canary. The issue does not affect production and is not currently blocking deployments.

Causes: Recent changes to ActionCable feature flags required a rolling restart of staging environments. The restart was not performed after toggling the 'use_primary_store_as_default_for_action_cable' flag, which may have contributed to the test instability.

Response strategy: We re-enabled the relevant ActionCable feature flag use_primary_store_as_default_for_action_cable and performed rolling restarts of the gstg-cny and gstg environments. We are monitoring ongoing test runs to confirm stability.

This ticket was created to track INC-6498, by incident.io 🔥