Lost in the shuffle means that something was overlooked, forgotten, or not noticed because there were many other things happening at the same time.
The image behind the expression comes from shuffling cards. When cards are mixed together, it becomes difficult to keep track of one particular card. That idea later became a useful way to talk about modern situations where a message, task, or person is missed in the middle of a busy group of items.
People often use this expression for work, school, family life, and administration. It usually suggests that the thing was not ignored on purpose. Instead, it disappeared among many competing messages, tasks, or requests.
- Her application got lost in the shuffle when the office moved.
- During the busy launch week, a few customer questions were lost in the shuffle.
You can also use it for people, not just paperwork. For example, a quiet student in a large class might feel lost in the shuffle if the teacher has too many students to notice every concern right away.