I'm not familiar with exactly how the Trek awards work, but it looks to me like the Milestone Award is triggered as a book level award, not a cumulative award. Go to Admin > Awards > Book Awards. (Note: in the Windows app, the Awards tab is under Admin > System Settings.) Choose the "Book-specific Awards for all grades". Select Trek for the Base Club and the appropriate book and review the awards listed there. If you have it set to trigger as a cumulative book award, it may also be triggering from the book-specific settings causing the two instances of the award.
Let us know if this helps resolve the problem.