It is derived from an issue I debugged a while back, where user was getting issues while creating an Incident through integrations where they had mapped some custom app field values to the OOTB ITSM Incident module field values.
And after debugging, it was found that, the issue was, they passed the priority field value but did not pass the priority weight, and the system expected the priority weight also as the priority was passed and not computed. I do not have the exact workflows now to share that caused the issue.
However the solution was to not pass the priority or priority values.
Rather pass the Impact and Urgency values and let the system compute the Priority and Priority weight values.