CCR and CCA failing to start for PR comments
This summary is created by Generative AI and may differ from the actual content.
Overview
On May 7, 2026, between 04:12 UTC and 06:13 UTC, Copilot Cloud Agent (CCA) and Copilot Code Review Agent (CCR) sessions for pull‑request comments were delayed or failed to start. The delay stemmed from replication lag on several database replica hosts that were introduced by a large migration performed as part of recovery work from a prior pull‑request incident.
Impact
The replication lag caused the internal pull‑request background processing pipeline to pause, preventing the events that trigger Copilot agents from being generated. As a result, some pull‑request comment processing was delayed and agents did not start until the replicas caught up. No quantitative metrics (e.g., number of affected PRs) were provided in the postmortem.
Trigger
A large database migration executed during the recovery of a previous incident introduced significant replication delays on replica hosts. The system’s safeguard interpreted the elevated replication lag as a signal to throttle writes to the affected database cluster, which in turn delayed the pull‑request background jobs that drive Copilot agents.
Detection
Monitoring systems flagged increased replication lag and reports of degraded performance for GitHub services. On‑call engineers were paged, and the incident timeline was tracked via status page updates indicating investigation and mitigation steps.
Resolution
When replication lag returned to normal levels, the pull‑request processing pipeline resumed, allowing the internal events to be emitted and the Copilot agents to start. The team continued to monitor the system to confirm full recovery and stability.
Root Cause
The root cause was the interaction between the safeguard that slows writes when replication lag is high and the recovery‑phase database migration that caused the lag. This combination temporarily throttled write traffic, delaying the background processing that initiates Copilot agents.