一度に and 一回: a batch together and one occurrence
Compare moving five sheets together with moving something once, separating the size of a batch from the number of actions.
Handling a group all at once
一度に, read いちどに, can mean all at once. 五枚の紙を一度に運びました。 says that five sheets of paper were moved together.
三人が一度に質問しました。 says that three people asked questions all at once. 一度に identifies the timing that groups their actions.
Counting an action’s occurrences
一回, read いっかい, means one occurrence. この機械を一回使いました。 says that this machine was used once.
荷物を一回運びました。 says that luggage was moved once. It does not specify that there was only one item of luggage.
Quantity and number of actions
In 五枚の紙を一度に運びました。, 五枚 supplies the number of sheets and 一度に says they were moved together. The two expressions supply different information.
一回で全部運べました。 says that everything was successfully moved in one go. 全部 identifies the full quantity; 一回で identifies the number of moves.
Does 荷物を一回運びました。 require the luggage to consist of one item?
Show the answer and why
No. It says that luggage was moved once. The number of items is not stated.