The NYT covered the story today:
A technical error in one of the engines prompted the landing on Dec. 14, a spokesman for Norwegian Air said by phone on Tuesday, and the 186 passengers and six crew members on board were unharmed. They spent the night in Iran and flew to Oslo the next day.
But things are more complicated for the plane. The spokesman said that Norwegian Air had never before dealt with regulations on the ground in Iran, and that the paperwork for anything from getting engineers to spare parts was taking longer than usual. He did not give an estimate of when the plane might take off again.
https://www.nytimes.com/2019/01/09/w...n-air-jet.html