When a job is started in NC, it usually has a process tree. Sometimes, the vovslaveroot process may stop unexpectedly or be killed; this creates orphan processes. A job process becomes disconnected from NC, but it still depends on that process to update the job object in NC vovserver's memory.
There is an -orphans option in the vovprocessmgr command that can find such processes and help account for the capacity they use on NC vovslaves. Use the command's help output and documentation for more details, like finding processes of a specific age or older.