The EN text is "The number of completions required to finish the minimog challenge has increased by 1 ([n] remaining)." The use of the term "completions" in this context is perhaps not the best choice, as the sentence is worded as though one additional event of the type in question must now be completed to finish the challenge (making it a literal Sisyphean task).

Something as simple as "Minimog objective completed! ([n] remaining)" would probably be both clearer and more concise. "sub-objective?" I don't know, just not "completion"