You have created a Custom Party on the Party Role Definition activity in Business Configuration and this is not being determined on the objects.
SAP Cloud for Customer
The Custom Party is maintained on an object different than the Account.
Custom Parties will only be determined from the Account. Example: When creating a Contract, you maintain Account and Ship-To. The Custom Party you created is on the Ship-To of the Contract. On saving, the Custom Party is not determined.
This is the expected system behavior.
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