I was modifying an LTN combinator during a blocking autosave, and likely pressed Enter twice after editing a request value (setting one of the data cards to -1000 in the linked save.)

As soon as the autosave completed, I got the following error:

Exception at tick 67302001: The mod LTN Combinator Modernized (1.0.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event LTN_Combinator_Modernized::on_gui_confirmed (ID 144)
__LTN_Combinator_Modernized__/script/gui.lua:101: attempt to index field '?' (a nil value)
stack traceback:
    __LTN_Combinator_Modernized__/script/gui.lua:101: in function 'set_new_signal_value'
    __LTN_Combinator_Modernized__/script/gui.lua:303: in function 'handler'
    __flib__/gui.lua:390: in function <__flib__/gui.lua:376>

Loading the save causes different issues, which I've reported separately. I'm not sure if the save is helpful for this particular crash, but it's here: https://drive.google.com/file/d/1wUc_nHaUL6fzboazlsJMbU-atDNJNd7y/view?usp=sharing

I haven't been able to reproduce exactly this, but I added a few checks and fixed a fundamental issue with save/reload safety. Marking this as fixed, but please let me know if you see this corner case again.