[Superman]

This looks like Fanuc codes
Are you sure that your 4th axis is "U" ???

A is the designated rotary axis around X
B around the Y
C around the Z

U is normally an incremental linear axis parallel to X

Check your manuals

A0 should replace the 1st U0
A180 replace the 2nd U0

Another suggestion- try replacing G80 with G0 ( G80 on some machines forces the spindle to stop )

G21
G0 G17 G40 G49 G80 G90
( 10. SPOT DRILL | TOOL - 10 | DIA. OFF. - 10 | LEN. - 10 | TOOL DIA. - 8. )
( SPOT DRILL ALL HOLES TOP )
T10 M6
G0 G90 G54 X-8.452 Y18.126 A0. S2000 M3
G43 H10 Z100.
M8
G98 G81 Z-1.5 R5. F50.
X0. Y20.
X20. Y0.
X0. Y-20.
X-20. Y0.
G0
G91 G28 Z0. ( Clearance safe )
( SPOT DRILL HOLES 6MM )
G0 G90 G55 X-20. Y0. Z5. A180.
Z100.
G98 G81 Z-1.7 R5. F50.
X0. Y20.
X20. Y0.
X0. Y-20.
G0
M9
M5
G91 G28 Z0.
G28 Y0. U0.
M30
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