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Hi, i'm not quite sure why your Kossel is acting up. I think there is something wrong in the line:

"G1 F{speed_travel} Z+1 E-1 ;move Z up a bit and retract filament even more"

and I think the whole sequence of your G-Code is a little bit wrong.

Here is my Start and End G-Code for an Anycubic Kossel Linear Plus using Cura 4.8.
Try it, it works well for me. I have no problems with rectraction etc.

Start G-Code:

;Start GCode
G21 ;metric values
G90 ;absolute positioning
M107 ;start with the fan off
G28 ;move to endstops
G92 E0 ;zero the extruded length
G1 F200 E3 ;extrude 3mm of feed stock
G92 E0 ;zero the extruded length again
G1 F{speed_travel} ;Put printing message on LCD screen
M117 Printing...

End G-Code

;End GCode
M104 S0 ;extruder heater off
M140 S0 ;heated bed heater off (if you have it)
G91 ;relative positioning
G1 E-1 F300 ;retract the filament a bit before lifting the nozzle, to release some of the pressure
G1 Z+0.5 E-5 X-20 Y-20 F{speed_travel} ;move Z up a bit and retract filament even more
G28 ;move to endstop
M84 ;steppers off
G90 ;absolute positioning

Cheers and good luck, Jay