Auctioning Operations are executed in the order they are assigned to a group. If you have multiple operations they will each attempt to post items according to the parameters defined in the operation in consecutive order.
For example, the first operation you have applied to a group may be attempting to post a total of 20 items per the parameters defined, then the second operation applied to the group may be attempting to post a total of 50 items. If you only have 5 of the item on hand, the first operation will post the 5 and you now no longer have enough items in your bags for the second operation to post anything.
Rearranging or reordering the order in which your Auctioning Operations are applied will help you post your items per your preferences.