Weakness in some central areas of the obverse and reverse are common among the coins of the Arkansas series.
On the obverse, I would check the cheek area of Miss Liberty as well as the area above her eye and below the Liberty cap (e.g., look for softness in the hairlines). I've seen a number of coins with a cheek that displays quite a few "chatter" marks that I view as un-struck planchet (i.e., a weak strike) vs. bag marks or other post-strike contact marks.
On the reverse, the head/neck/chest areas of the eagle often show some weakness (i.e., some indistinctness in the feathers). These areas should definitely be inspected closely when considering an Arkansas half-dollar for purchase.
I've seen quite a few "flat" Arkansas coins, even in higher grades (MS65/66); by this I mean coins with dull and lifeless surfaces (likely due to being over-dipped in their past). I've passed on quite a number while in searching for a coin with a reasonable strike and nice cartwheel luster. If you are looking for one, I would definitely hold out for an Arkansas with good luster and details in the areas noted.
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