ORA-02374 (IMPORT DATAPUMP)

I'm getting ORA-02374 (conversion error loading table) but the length of the column (varchar2(4000 CHAR)) is sufficient. A few rows cannot be inserted.

ORA-02374: conversion error loading table "..."."..."

ORA-12899: value too large for column FORMULA (actual: 4000, maximum: 4000)

ORA-02372: data for row: FORMULA : 'bankID=..., clientID=..., columnNames=[IC'

I do not understand this behaviour, has anybody an idea or recommendations for me?

Additional Information:

Patchlevel: Source-DB-Version: 19.9

Patchlevel: Target-DB-Version: Database Release Update : 19.11.0.0.210420 (32545013)

Column_name= FORMULA

Both Datatypes are VARCHAR2(4000 CHAR)

Error is thrown only when length(FORMULA) = 4000