Hi Sajan,
did you check if the Cluster B2 of database table PCL2 was archived for this few employees with Transaction PU22 or Report RPUARTX0? In this case you can use the Option Display archived in Transaction PT_CLSTB2 - Show (Cluster B2) to show the old results.
Otherwise may be somebody edited/deleted the Cluster from the database PCL2 manually. Please check if SE16N or and other report was used to delete the time evaluation for these employees.
It is also possible, that somebody changed infotype 0007 (Planned Working Time) for this few employees to "0 - no time Evaluation, so that a retroactive accounting date was set in infotype 0003 and next time evaluation started a retroactive accounting which deleted the time evaluation. Check the changes of the infotype with Report RPUAUD00
Greetz
Andy