One of the reasons why the middle items in a long list of items are less likely to be accurately recalled than items at the beginning and the end of the list is because the middle items

Because the middle items  do not benefit from either the recency or the primacy effect the beginning and the last items in the long list are more likely to be recalled because our memory could easily distinguish the situation during initial memorizing process and the situation where the process is about to end, while noting really give a certain anchor for what happening in the middle of the process.