Docker Engine version inconsistencies within a Swarm cluster can cause subtle traffic degradation. This issue manifested on a manager node with Traefik reporting a service as unavailable. The suspected cause was differing iptables rules and overlay networking between Docker versions 28.1.1 and 28.2.2. This precise problem occurred in the production environment of a major public transportation app on June 22, 2025. The application supports approximately 2 million users with tens of thousands of daily active users. The system handles a substantial load of 1000-1600 requests per second. Partial traffic issues at a single entry point significantly impacted a high-traffic segment. Without timely localization, this degradation could have negatively affected SLA metrics. The scenario highlights the critical importance of consistent Docker Engine versions in production Swarm environments. Maintaining uniformity prevents hidden performance issues and ensures service stability for large user bases.