That looks very strange to me. If the datatype in HANA of AEDAT_Last_Changed_on is really nvarchar(8) and its values are stored as YYYYMMDD, a to_date(<input string>,'YYYY-MM-DD') will never work.
I suspect it has datatype date. The to_date function expects a first parameter of type char. Because the type is not correct, an implicit to_char function is applied first with default format YYYY-MM-DD.
Can you doublecheck?