The line

my $dt = $Strp->parse_datetime($1);
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is returning undef because the input string in $1 is in an incorrect format. Either change the declaration of Strp like

my $Strp = new DateTime::Format::Strptime(pattern     => '%Y-%b-%d %T'
+, on_error => 'croak');
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to throw an error in that case or check for it in your code by replacing the line starting 'my $dt...' with

unless (my $dt = $Strp->parse_datetime($1))
{
  warn "invalid datetime: $1";
  next;
}
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