This is great advice. I'm using Cura and Octoprint. Since I moved our tree forward against the upstream/master, I've noticed the Waiting for user message has changed to M105. M105 is the temperature poll for the extruder (IIRC). I think I am having a timeout issue with my Octoprint settings.

what does your cura start gcode look like? mine is like this

;Sliced at: {day} {date} {time}
;Basic settings: Layer height: {layer_height} Walls: {wall_thickness} Fill: {fill_density}
;Print time: {print_time}
;Filament used: {filament_amount}m {filament_weight}g
;Filament cost: {filament_cost}
M190 S50 ;Uncomment to add your own bed temperature line
G21 ;metric values
G28
G29
M109 S225 ;Uncomment to add your own temperature line
G90 ;absolute positioning
M82 ;set extruder to absolute mode
G1 Z15.0 F{travel_speed} ;move the platform down 15mm
G92 E0 ;zero the extruded length
G1 F200 E3 ;extrude 3mm of feed stock
G92 E0 ;zero the extruded length again
G1 F{travel_speed}
;Put printing message on LCD screen
M117 Printing...