This is a bug from the software.
You must deactivate the "SHARE TEMPERATURE'"
You can have 1, or 2 or 3 extruders.
After, at the top of the soft, you can see 2 or 3 extruders , where you must set the T° to ZERO °C , for extruder 2 and extruder 3
For me, i have the Geeetech A20M... and it was so long to find this "stupid idea"
Now it works ...
I could add my Geeetech A20M , using the "prusa i3 preset", and add 2 extruders.
I use my Geeetech with ESP3D to print by Wifi for small pieces. and by Sdcard for long time prints.