LR4 Z0 Drops During Surfacing Spoil Board

O.K…I’m running a small surfacing code. Surfacing a 12x18" piece. First pass is from the right side to left, at 1mm doc.
Y moves for the overlap, and Z0 drops approx. 0.5mm and then cuts left to right
Y moves for the overlap, Z0 does not move, and cuts right to left
Y moves for the overlap, Z0 drops approx. 0.5mm and cuts left to right

This happens for 3 successive left to right cuts only.
I use Vetric Vcarv Pro V12 to generate Gcode (see below)

(VECTRIC POST REVISION)
(904C316D3FF9436FDB18E2DEC4010178)
G21
G90
G94
G92 X0 Y0
M0 (MSG Attach probe)
G38.2 Z-80 F200 P0.5
G1 Z50 F900
M0 (MSG Remove probe, turn on vent, turn on router)
M62 P1
S10000M3
G0X458.490Y16.510
G0Z10.000
G0Z5.000
G1Z-1.000F177.8
G1X1.510F3810.0
G1Y35.560
G1X458.490
G1Y54.610
G1X1.510
G1Y73.660
G1X458.490
G1Y92.710
G1X1.510
G1Y111.760
G1X458.490
G1Y130.810
G1X1.510
G1Y149.860
G1X458.490
G1Y168.910
G1X1.510
G1Y187.960
G1X458.490
G1Y207.010
G1X1.510
G1Y226.060
G1X458.490
G1Y237.490
G1X1.510
G0Z10.000
G0X462.300Y12.700
G0Z5.000
G1Z-1.000F177.8
G1X-2.300F3810.0
G1Y241.300
G1X462.300
G1Y12.700
G0Z10.000
M63 P1
G0 x0y0
M2

Any help greatly appreciated. I’m at a loss.