Error KI 249 upon PR creation pointing into Profitability Segment

Dear Colleagues,

I get an error KI 249 during PR creation and it seems like the reason for the error is a WBS and a Profitability Segment assignment at the same time. While I do assign WBS manually, it is not clear how the Profitability Segment gets assigned and how can I see it from the PR before saving the data. It is an account based PA in S/4HANA, and the project profile behind the WBS is not part of COPA derivation settings, which confuses even more.

Thank you,

Paulo