Sometimes text files (presumably 'wrapped' onto more than one line per single record in the input file for Monarch) do not have an end of line or end of file 'marker' that Monarch recognises at the end of the very last line. The last line but one is recognised.
Could this be the case here?
If you edit a test copy of the txt file to add an extra line - a single character will do - do you get your data?
(I am assuming you are using 'character' and 'columns' interchangeably in your description so that your record length is 397 in total.)
There are some very helpful tools at:
"Examine", "FilePart" and "Prep" might all be helpful here.
Examine will tell you what strange characters might be causing the problem. You might find that in Monarch, editing the Input settings in the Options menu so that Monarch ignores non-printable control characters would also help.
If you have 397 columns of data, as opposed to a report 397 characters wide, then we have a different issue, as Monarch only supports 254 fields in any model...