Hi,
Just out of the blue mod starts throwing errors when you try to choose item to request/provide:
The mod LTN Combinator caused a non-recoverable error.
Please report this error to the mod author.

Error while running event LTN_Combinator::on_gui_elem_changed (ID 67)
Unknown elem type.
stack traceback:
LTN_Combinator/scripts/ltnc-gui.lua:364: in function <LTN_Combinator/scripts/ltnc-gui.lua:363>
stack traceback:
[C]: in function 'index'
__LTN_Combinator/scripts/ltnc-gui.lua:364: in function <LTN_Combinator/scripts/ltnc-gui.lua:363>

It worked in this save game. I am using Krastorio and bunch of QoL mods.

Hi,

that is a bug with factorio introduced in 17.61: https://forums.factorio.com/viewtopic.php?f=30&t=73996

If you can't wait for the update you can disable the LTNC-Gui in the Mod-Settings:
Mod Settings -> Map -> LTN Combinator -> Disable mod on version mismatch

That way the gui will be disabled and you can work with the default combinator interface