I was on a Norwegian plane once going from Oslo to London, 3/4 into the journey, just before descending into Gatwick, we got told the plane is turning around due to fault on the plane. So deflating when you are nearly home. The pilot did a good job calming everyone down and explaining it was a minor fault, two duplicate sensors were showing different values, but still, enough to recall the plane.
So basically another 1.5h flight back to Oslo, a few hours wait, then on a replacement plane (thank god) with another flight back to London. A long day.
I can, however, understand it. As with this 737 Max-8s they did not want the plane grounded in an airport where they don't have a full service centre with parts etc. Had it only been a few years later we could have continued as they made Gatwick one of their major hubs with probably full stock of parts.
Though I do have a rule of preferring flying out from an airport with a "local" airline, as they are quite likely to have parts and chances of spare or frequent incoming planes to shuffle around to.
Related, Norwegian plane was stuck in Iran: https://eu.usatoday.com/story/travel/flights/2019/01/10/norw...