When did initial indicators of trouble with the RCS thrusters surface for Starliner?

Shortly after Starliner successfully docked with the orbiting outpost

The detection of anomalies with the capsule’s attitude control mechanisms occurred subsequent to reaching the orbital destination. Specifically, the initial indicators that several of the small engines used for orientation—the RCS thrusters—were not performing to expected parameters surfaced during the maneuvers necessary for docking with the International Space Station (ISS). Although the issues were noted immediately after docking, they did not constitute an immediate life-threatening situation, as the capsule was able to maintain a safe configuration while berthed to the station, allowing engineers time to commence the deep dive into the telemetry data.