It is not just hitting anything.
C/F does not always have the tightest tolerances.
The thickness can vary quite a bit within one sheet.
When you are cutting many small arms out of one sheet, the actual thickness of each arm can (and will) differ signifcantly.

So when you receive your 2 arms in the kit (or purchase replacement arms after), chances are they won't be the exact same thickness. This can alter your front suspension from left to right some (one may have more flex than the other).

With my Corally, I used to have to go through multiple amounts of arms to find 2 with similar thicknesses.

Plus the thin ones will break with good contact.