We moved away from Siemens do to their Arc Fault issues. There are so many different generations of breakers that it's tough to say what version they have and if replacing it will fix the problem. Basically each generation has improved their arc signature recognition but it still never solves every problem. David asks the question about the number of lights being dimmed on that particular circuit (not just the switch) because there is a max wattage per breaker (typically 1000 watts). This number is tough to reach with LED but super easy with incandescent lighting.

Long story short, it's the breaker and you may not be able to fix the problem by replacing the breaker unless it's an older gen arc fault breaker. The only fix is illegally pulling out the arc fault breaker and installing a standard breaker. Which we all know will work fine. The question is, do you want to take the liability on if there is a fire....

Could also be a breaker issue. We (as an electrical contractor) have seen very sensitive AFCI breakers (typically when combined with GFCI protection). I would suggest installing a standard breaker and add a faceless AFCI receptacle [Link: leviton.com] at the panel. This will still meet the code requirement but bypass the sensitive breaker.