3733339 - How the fallback strategy works in actual costing run

Question on why the system apply fallback strategy to determine previous period Periodic Unit Price(message C+136) or Current period standard price(message C+137) as current period Periodic Unit Price.

SAP S/4HANA Cloud Public Edition

If the cumulated difference is too low (negative), it may cause the actual value (prerequisite + difference) become negative. Since this is not reasonable to have negative actual value, system will use fallback strategy to determine the actual value.
   The PUP is calculated with these priorities and you normally get relevant messages:
    1. 'Cumulative Inventory' line (no fallback)
    2. Receipts ('ZU') line (Info message C+ 135 in the log)
    3. Beginning inventory ('AB') line  (Info message C+ 138 in the log)
    4. PUP-price of previous period (Info message C+ 136 in the log)
    5. S-price (Info message C+ 137 in the log).

For step 4, system trying to find the previous period periodic unit price(PuP) from all previous period where actual costing run is performed for that material. It will sort descending the period and try to find the PuP in sequence, if found, it will be used as current period PuP and raise message C+136,
if for example, actual costing is never performed before, it will use current period standard price as current period PuP.

MLRUNLIST, FMLT_PRICE, Fallback strategy, Not distributed, C+136, C+137. , KBA , CO-PC-ACT-2CL , Actual Costing (Public Cloud) , Problem