To reproduce:
- Put down a circuit
- Enable "packed mode"
- Add 20 input / output poles
- Exit Editor

Similarly, when you enable packed mode while having 20 input/output poles, it crashes as well.

78.466 Error MainLoop.cpp:1391: Exception at tick 19414: The mod Compakt circuits (1.0.28) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event compaktcircuit::on_gui_click (ID 1)
The mod Compakt circuits (1.0.28) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event compaktcircuit::on_player_changed_surface (ID 53)
compaktcircuit/scripts/build.lua:649: attempt to index local 'iopoint' (a nil value)
stack traceback:
compaktcircuit/scripts/build.lua:649: in function <compaktcircuit/scripts/build.lua:526>
(...tail calls...)
compaktcircuit/scripts/build.lua:808: in function 'create_packed_circuit'
compaktcircuit/scripts/editor.lua:1371: in function <compaktcircuit/scripts/editor.lua:1341>
[C]: in function 'teleport'
compaktcircuit/scripts/editor.lua:736: in function 'exit_player'
compaktcircuit/scripts/editor.lua:750: in function 'handler'
compaktcircuit/scripts/tools.lua:350: in function <compaktcircuit/scripts/tools.lua:346>
stack traceback:
[C]: in function 'teleport'
compaktcircuit/scripts/editor.lua:736: in function 'exit_player'
compaktcircuit/scripts/editor.lua:750: in function 'handler'
compaktcircuit/scripts/tools.lua:350: in function <compaktcircuit/scripts/tools.lua:346>

Thanks for reporting
Fixed in 1.1.0

Thanks for the quick reply, but it still happens when using CTRL-C/CTRL-V or blueprints to copy the input/output poles.

Sorry, the fix will be in the next release

Should be fixed in release 1.1.1

Awesome, thanks for the quick fix! :)