So I've been tweaking the Data Type in the Flat File Connection:
When all columns are set to DT_STR and width 200, the package fails on row 655 column 63
So I changed all columns to DT_TEXT:
The package still failson ro 655 column 63 with "The data conversion for column "Column 63" returned status value 4 and status text "Text was truncated or one or more characters had no match in the target code page"
Something very strange (and probably easy to fix) is going on.