Not exactly a bug, but... I couldn't think of a more appropriate place to put it.
Under the Arcade button, before anything is pressed, this is the first sentence:
Arcade Missions allow you to explore the ever-changing Clockworks without specific objective.
The last words should be "without specific objectives" or "without a specific objective".
Not significant, I know, I just couldn't leave it be :3
The sentence is actually still grammatically correct.
While both your suggested changes are also grammatically correct, they don't necessarily make the original sentence any more grammatical.