Bug? Danged If I Know

Basic Information:

Printer Model:
two trees sapphire 5
mks Robin_nano_V3.1:

Fill out above information and in all cases attach your klippy.log file. Pasting your printer.cfg is not needed
Be sure to check our Knowledge Base and in particular this and this post

Describe your issue:

Trying to get some clearance so I can brush a hot nozzle before starting a print, I’ve added some stuff to the startup stanza in cura 5.2.1 so that it runs the bed down a couple hundred mm’s, giving me time to brush the hot nozzle.
looks like this:
;Filament used: 49.2947m
;Layer height: 0.16
;Generated with Cura_SteamEngine 5.2.1
M140 S71
M190 S71
M104 S245
M109 S245
M82 ;absolute extrusion mode
M140 S75 ; set bed temp
M190 ; wait for bed temp
M104 S245 ; starting hot end temp
M109 ; wait for hotend temp
G90; absolute positioning
G28 ;Home all
G1 F750 Z200 ;room and time to clean nozzle
;M420 S1 ;Enable ABL using saved Mesh and Fade Height
G92 E0 ;Reset Extruder
G28 ;home all again
G1 Z2.0 F3000 ;Move bed down
M400; wait for this move to finish
G92 E0; rezero extruder
G1 X9.9 Y20 Z0.20 F5000.0 ;Move to start position
G1 X9.9 Y275.0 Z0.20 F1500.0 E17 ;Draw the first line
G1 X10.3 Y275.0 Z0.20 F5000.0 ;Move to side a little
G1 X10.3 Y20 Z0.20 F1500.0 E33 ;Draw second line should merge
G92 E0 ;Reset Extruder
G1 Z2.0 F3000 ;Move Bed down
; lift start line, measure for.20mm!!!
G92 E0
G92 E0

Cura code to lay skirt follows.
Printer starts up ok, But something is killing the heat, so the print dies in the middle of the skirt due to hotend under temp. I look at controller and both heat tally leds are being turned off by something in the above g-code.
It might be the M400, I’ve had the same effect using a G4 S60, a command I’ve never had similar results with when I’ve used it on machines I’ve built using LinuxCNC as the driver. G4 is supposed to be a pause, but never shut down something that has been previously enabled, it simply pauses all activity until S or P time has expired.

Have I found a (gasp) bug?

Cheers, Gene
Or is there something else in the above g-code shutting off the heat?

Can you please format the code with

Else there is no hint for shuting down the heaters in that code.

Would you please share the klippy.log as file in your next post.