You are facing different pricing using the same pricing procedure in different billing documents due to missing conditions.
S/4 HANA Cloud All versions
Reproducing the Issue
1. Display Billing Documents App.
2. Display both documents price analysis.
3. One document have found the condition record, the other don't.
Condition record is missing in the billing document since the Rendered Date is out of Condition Record time period scope. You can check within the Price Analysis, within the missing Condition Access, the Serv. Rendered Date and compare with the one maintained in SSCUI 101120.
Maintain condition record valid period within SSCUI 101120.
KBA , SD-BF-PR , Pricing , Problem