You need a pattern specification that does not contain or inject those vertical lines, such as this one built assuming a block size of 75x600mm:
;-------------------------------------------------------------------------------
; Written by HatchKit 4 Standard Edition
; HatchKit 4 Standard Edition (c)1990-2020 Cadro Pty Ltd
; www.hatchkit.com.au/
;-------------------------------------------------------------------------------
;-Date : 2020-12-17
;-Time : 15:40:10
;-HatchKit 4 Version : 4.0.9.2894
;-------------------------------------------------------------------------------
;%VERSION=3.0
;%UNITS=MM
*Entities,DXF Entity Section
;%TYPE=MODEL
0,0,0,0,75
90,750,75,-450,150,75,-1125
90,600,0,-450,150,75,-1125
90,150,75,-450,150,75,-1125
90,0,0,-450,150,75,-1125
hth,
Hugh Adamson
www.harchkit.com.au