The "Main Assignment" indicator is not maintained consistently

What causes this issue?

A main assignment is only consistent if the relevant assignments are
located within the same category and the validity periods form an
uninterrupted series. You must have defined at least one assignment as a
main assignment.
These conditions have not been met with the current assignments, that is
to say, either assignments in different categories were defined as the
main assignment, the defined assignments are located within the same
category but do not form an uninterrupted series, or no assignment was
defined as the main assignment.
In addition, the valid-from date of a main assignment cannot be in the
future.
Continued maintenance is only possible in article hierarchy maintenance.

System Response

The system did not transfer the entered assignments.

How to fix this error?

Define the main assignments in such a way that the above conditions are
met and the required consistency is achieved.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.