What issue arose during the flight from Grand Cayman to MCO?

The issue that arose during the flight from Grand Cayman to MCO was related to the FMS (Flight Management System) screen being unreadable. This situation indicates a potential technical malfunction or error that could significantly impact flight operations by hindering the pilots' ability to access vital navigation and flight planning information. The FMS is crucial for managing the flight trajectory, including waypoints, altitude, and speed, so a lack of visibility on the display would impede a pilot's ability to operate the aircraft effectively and safely.

In this context, the other options suggest various mechanical or operational challenges that could occur during a flight. However, the FMS screen being unreadable presents a direct challenge to necessary functions for navigation and safety, making it the most pertinent issue among the choices provided. It highlights the importance of having functional electronic navigation systems in modern aviation.