Thanks for the quick update.
A crash occurred while upgrading several entities, see screenshot below.
Edit: Can reproduce it when upgrading yellow underground belt to red underground belt.

6170.429 Error MainLoop.cpp:1475: Exception at tick 1921791: The mod Updated Construction Drones - Forked (1.1.10) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Construction_Drones_Forked::on_ai_command_completed (ID 136)
LuaEntity doesn't contain key neighbours.
stack traceback:
    [C]: in function '__index'
    __Construction_Drones_Forked__/script/command_processor.lua:861: in function <__Construction_Drones_Forked__/script/command_processor.lua:836>
    (...tail calls...)
    __core__/lualib/event_handler.lua:72: in function <__core__/lualib/event_handler.lua:70>
6170.429 Error ServerMultiplayerManager.cpp:85: MultiplayerManager failed: "The mod Updated Construction Drones - Forked (1.1.10) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Construction_Drones_Forked::on_ai_command_completed (ID 136)
LuaEntity doesn't contain key neighbours.
stack traceback:
    [C]: in function '__index'
    __Construction_Drones_Forked__/script/command_processor.lua:861: in function <__Construction_Drones_Forked__/script/command_processor.lua:836>
    (...tail calls...)
    __core__/lualib/event_handler.lua:72: in function <__core__/lualib/event_handler.lua:70>"

This issue should be fixed. there was a change to how underground belts are handled in 2.1

Still crashes when upgrading yellow underground belt:

  27.428 Error MainLoop.cpp:1475: Exception at tick 4057211: The mod Updated Construction Drones - Forked (1.1.11) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Construction_Drones_Forked::on_script_path_request_finished (ID 135)
LuaEntity doesn't contain key underground_neighbour.
stack traceback:
    [C]: in function '__index'
    __Construction_Drones_Forked__/script/command_processor.lua:861: in function <__Construction_Drones_Forked__/script/command_processor.lua:836>
    (...tail calls...)
    __Construction_Drones_Forked__/script/event_processor.lua:322: in function 'handler'
    __core__/lualib/event_handler.lua:72: in function <__core__/lualib/event_handler.lua:70>
  27.428 Error ServerMultiplayerManager.cpp:85: MultiplayerManager failed: "The mod Updated Construction Drones - Forked (1.1.11) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Construction_Drones_Forked::on_script_path_request_finished (ID 135)
LuaEntity doesn't contain key underground_neighbour.
stack traceback:
    [C]: in function '__index'
    __Construction_Drones_Forked__/script/command_processor.lua:861: in function <__Construction_Drones_Forked__/script/command_processor.lua:836>
    (...tail calls...)
    __Construction_Drones_Forked__/script/event_processor.lua:322: in function 'handler'
    __core__/lualib/event_handler.lua:72: in function <__core__/lualib/event_handler.lua:70>"

Are you on 2.0 or 2.1?

Nevermind. I used AI to parse the docs and it gave underground_neighbour instead of underground_belt_neighbour
I verified its working properly now

Can confirm, working now.
Thanks for the fixes and for keeping the mod updated!