Occurrs when upgrading (via auto-building) the last segment of a conveyor belt (blue) leading out of a modded splitter (belt balancer 2)

I was able to reproduce it successfully every time.

The mod Lazy Builder (1.0.6) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event auto-build-and-deconstruct::on_tick (ID 0)
The mod Belt Balancer 2 (2.0.9) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event belt-balancer-2::script_raised_built (ID 87)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__belt-balancer-2/objects/balancer.lua:140: in function 'recalculate_nth_tick'
belt-balancer-2/objects/belt.lua:239: in function 'built_belt'
belt-balancer-2/control.lua:111: in function <belt-balancer-2/control.lua:94>
stack traceback:
[C]: in function 'create_entity'
auto-build-and-deconstruct/control.lua:153: in function 'upgrade'
auto-build-and-deconstruct/control.lua:56: in function 'scan'
auto-build-and-deconstruct/control.lua:23: in function <auto-build-and-deconstruct/control.lua:20>

I was able to produce a similar crash when disconnecting some of the inputs. it would upgrade without crashing but would immediately crash upon pressing the undo button.

The mod Lazy Builder (1.0.6) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event auto-build-and-deconstruct::on_tick (ID 0)
The mod Belt Balancer 2 (2.0.9) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event belt-balancer-2::script_raised_revive (ID 89)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__belt-balancer-2/objects/balancer.lua:140: in function 'recalculate_nth_tick'
belt-balancer-2/objects/belt.lua:218: in function 'built_belt'
belt-balancer-2/control.lua:111: in function <belt-balancer-2/control.lua:94>
stack traceback:
[C]: in function 'revive'
auto-build-and-deconstruct/control.lua:116: in function 'construct'
auto-build-and-deconstruct/control.lua:60: in function 'scan'
auto-build-and-deconstruct/control.lua:23: in function <auto-build-and-deconstruct/control.lua:20>

will crash even with some of the belts disconnected.

The mod Lazy Builder (1.0.6) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event auto-build-and-deconstruct::on_tick (ID 0)
The mod Belt Balancer 2 (2.0.9) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event belt-balancer-2::script_raised_revive (ID 89)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__belt-balancer-2/objects/balancer.lua:140: in function 'recalculate_nth_tick'
belt-balancer-2/objects/belt.lua:218: in function 'built_belt'
belt-balancer-2/control.lua:111: in function <belt-balancer-2/control.lua:94>
stack traceback:
[C]: in function 'revive'
auto-build-and-deconstruct/control.lua:116: in function 'construct'
auto-build-and-deconstruct/control.lua:60: in function 'scan'
auto-build-and-deconstruct/control.lua:23: in function <auto-build-and-deconstruct/control.lua:20>

It would appear there is some sort of glitch happening. I was able to get the game to not crash when doing the same but without any other input or output belt, however, upon undoing the upgrade with the CTRL+Z hotkey, it will skip the undo and instead undo the next action.

Hello, thanks for the bug report.
I'll fix it as soon as possible.

It would appear there is some sort of glitch happening. I was able to get the game to not crash when doing the same but without any other input or output belt, however, upon undoing the upgrade with the CTRL+Z hotkey, it will skip the undo and instead undo the next action.

test pls