When we first make the suppository, we must leave a small air space on the top to facilitate sealing. Therefore, the suppository is not 100% full. there is a small space on the top. Otherwise, the suppository cannot be sealed.
In summertime, due to hot weather, suppositories might be melt during shipment or seating in a hot mailbox. The air space previously on the top space can be relocated to one site. You may think that is an air bubble. The product can reset once in a cooled environment like a refrigerator. The total mass is not reduced and the quality is unchanged even though the shape may change.
Please do not worry about. You may find these articles helpful: