Pavers rarely fail on their own. When an area dips, rocks underfoot or holds water, the base beneath it has moved, washed out or was never compacted correctly.
Common causes
Insufficient base depth, poor compaction, water running toward the surface instead of away from it, missing edge restraint letting the field spread, or a settled utility trench beneath the surface.
What a real repair looks like
The affected pavers are lifted and set aside, the base is rebuilt and re-compacted to the correct depth, grade is corrected, and the original pavers are reset with new joint sand. Done properly, the repaired section is indistinguishable from the rest.
When resetting beats replacing
If the pavers themselves are in good condition, resetting is usually the cost-effective option and keeps the original material and pattern intact.