I have printed and sliced your stl with luban.
I see nearly the same travelpaths but finally i have no strings between or inside the B, 6 or 9.
Retract at Layer Change: NO
Retraction Distance: 1mm
Retraction Speed: 45mm/s
Z-Hop when retracted: NO
Printed with well calibrated PETG in 3mins.
Now i tried your gcode and got the same results like you.
My final research is that only editing the retraction speed did the same, you need to retract less.
Try it with 1mm retract distance at 45mm/s.
(Maybe you also need to print higher layers, thats what i guess too, but have no more time to test now, i am on the jump to vacation =)
Hope this helps!