You use the automatic settlement rule generation for WBS elements. The restriction of the maximum number of distribution rules in the settlement profile is not taken into account when a new distribution rule is created. Additional key words
In the master data maintenance (for example, in the Project Builder - Transaction CJ20N), the number of the distribution rules is checked correctly.
CJB1, CJB2, KSRG, LKSRGF02, K_POSTING_RULE_INSERT Cause and prerequisites
The check is not complete. Solution
https://service.sap.com/sap/support/notes/409231 (SAP Service marketplace login required)