Actual Cost alculation

Hi,

We are using Oracle OPM Financials R12.1.3. I want to know that, is there any criteria that is used to include an item in cost update process. What we find here, the system calculates actual cost for same items intermittently. For some periods its cost is calculated, and for other periods its cost is null. We run actual cost and cost update process just before closing periods

For example: system has calculated the actual cost for an item x from Jan 14 to May 14, and thereafter its actual cost column is showing null value despite we have run all processes