Dynamic Flat File Import uses wrong THUNK_COLUMN length.
It appears that the column length is being picked up from whatever we set the THUNK_COLUMN length against the Flat File Connection manager rather than the destination table individual column length's.
Set the THUNK_COLUMN column type to DT_WSTR and length to 250 in the Flat File Source component.
When column length is set to DT_WSTR and length 250 for the flat file source, the code will trigger to configure the source column type to match the destination column.
For database destinations, that process works. However, if the user connects flat file destination where there is no columns metadata, that algorithm doesn’t work well for the situations where the column length exceeds 250 characters. When the customer changes the source column length, the source columns length is no longer applied based on the destination. The changed column length in the flat file source will now be the default during the initialization.