Internal error in ANALYZE_ACT_FIELDCAT

What causes this issue?

An internal error has arisen in the form routine ANALYZE_ACT_FIELDCAT
for program RFITEM_INC.
This is due to inconsistencies between table T021S (special fields) and
structure RFPOSEXT.

System Response

During the processing of special fields in the line item list, errors
and even a program termination may occur.

How to fix this error?

Recreate the special fields in Customizing. If the error occurs again,
contact SAP.

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.