A little too much case lube is the cause of the dimple. It is very common in such calibers as 3030 loadings because the case is so thin, and just like yours it happens usually around the shoulder of the case. It will not hurt the casing, and is safe to shoot. At the most it will very slightly cut back on case capacity depending on if it is a compressed load, and the powder and charge weight used.
It will not affect chamber pressure, and will disappear on firing.