Investigate why workers utilizing load balancing, started to hit primary

We have noticed that one of the workers that utilize load balancing features, and uses replica for reads, started hitting the primary.

We enabled BuildHooksWorker to utilize load balancing features in gitlab-com/gl-infra/production#4377 (closed) on May 10th, 2021.

https://dashboards.gitlab.net/d/sidekiq-queue-detail/sidekiq-queue-detail?viewPanel=126[…]line_hooks:build_hooks&from=1622793791733&to=1622804917137

We can see that it started hitting the primary on Jun 4th. Before this date, it was always hitting only replicas, since we enabled the feature flag.

https://log.gprd.gitlab.net/goto/75fa6f63cc8b0780ba3a7a626771559c