Looks like there are perhaps more "//\n" strings in the data than you think.

If I create a data file by hand, your code works fine. Perhaps you should print out the records so you can see where it's breaking ?

$/="//\n";# no need to escape / .. not that it matters
open(FILE,$ARGV[0]) or die("Can't open $ARGV[0]: $!\n");
while (<FILE>) {
    chomp;
    # print the record between square brackets
    # and add an extra couple of newlines to make
    # it obvious where the record breaks are
    print "record #$. contains [$_]\n\n";
}
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