After going through the report it looks as if most of the loss came from restarting the whole operation after shutting it down in 2015. They had to suspend many operations which resumed in december 2017, this limited them from producing at full capacity due to a ramp up. The ramp up plan will now be executed in 2018 and continue onwards. Everything is coming along slowly but surely.
This article breaks down each aspect.
https://www.newswire.ca/news-releases/katanga-mining-announces-2017-fourth-quarter-and-year-end-financial-results-678575343.html