The airplane had the Air Iceland logo on the seat covers. Air Iceland does not fly to Norway, only Iceland, Greenland and the Faroe Islands.
When Vincent Rattrey (Luke Treadaway) entered the sauna room, he sat on the wood bench without a towel underneath him, covering the bench. That is 'violation' of sauna etiquette.
Vincent Rattrey is seen sitting naked on a wooden sauna bench. The temperature inside a proper Scandinavian sauna varies from 80 to 120 degrees Celsius (180 to 250 F). The wood inside the sauna has the same temperature. Moreover, natural resins in the wood accumulates even higher temperatures. Sitting naked on anything heated to those numbers becomes quite unbearable in a matter of milliseconds. Another goof is both him and another man entering sauna without covering their heads. Hot sauna air burns the ears so wearing a special felt hat is a must.
The town sign at the entrance to the settlement states the total population of Fortitude. This strange, chiefly US practice does not really exist anywhere outside the United States. The sign actually looks like it was just lifted directly off an US highway. European signs are standardized and look differently.
When Vincent see a dead body inside a house, he is standing on the outside. With the camera on the inside, one can see that the door handle is in open position. When he breaks the door window, however, the handle is in locked position.
(at around 39 mins) The northern lights appear underneath the cloud ceiling.