The ship has temporarily turned off its' AIS reporting equipment. This is not unusual especially when a ship is in port. AIS reporting equipment is required to be on 15 minutes prior to departure and remain on until the ship is once again docked at its' next destination.
The AIS reporting equipment onboard the ship requires maintenance. This is usually a temporary situation because onboard AIS equipment is a regarded as a safety device and is required to be in working order by International Maritime Laws.