Im part of a pvp guild where the requirement is to always have stone ballistas. They are costly, something anyone would notice if you havent played for long and try to gather up some AP for future updates.
During sieges I and others keep encountering strange bugs/lags where you pop a siege, and then it sometimes cant be used, it's just standing there. Eventually it breaks, or it can break right away. Often this feels connected to lags during big fights.
This weekend alone I bought 9 stone ballistas due to this, thats 16200 AP which is alot to me. If you look past the cost, it's still pretty stupid that majority of sieges is lost due to this "bug".