You have "variable length records". But
Here you copy from position 44 for a length of 419 bytes. Not all your records are the full length. Your records are not fixed in length.
What you need is:
This, as the last definition on the statement, says "copy from start position 44 to the end of the current record". With that code, you'll not get a "short record" unless any records on your file are less than 44 bytes long.