Of the available choices, more than one device sending traffic to a single destination at the same time is most likely related to microbursts occurring on a network. A microburst is a significant increase in traffic over a very short period of time that can result in packet loss.
If the buffer size is inadequate and the buffer limit is exceeded, packets are dropped. Reducing the buffer size would increase, not decrease, the negative effects of a microburst; increasing the size of the buffer is the most effective way of avoiding packet loss due to a microburst. However, even if the network administrator reduces the size of the buffer, that action in itself will not cause a microburst to occur. Although a shutdown interface might cause some packets to not reach their destination, a shutdown interface would not cause microbursts to occur on a network.