Hi, when I clicked a red loader I got the following error.

The mod Loaders Modernized (0.7.4) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event loaders-modernized::on_gui_opened (ID 95)
loaders-modernized/scripts/loader-gui.lua:127: attempt to index field 'players' (a nil value)
stack traceback:
loaders-modernized/scripts/loader-gui.lua:127: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

Was this the first time you loaded after upgrading? What version of the mod were you running before this?
Is this a multi-player game? Where you hosting / joining?

Were more than one player / robots interacting with the same loader?

Can you provide a save file this is demonstrating this behavior?

I have been using this mod since I factorio 2.0 came out. Never paid attention to clicking the loaders. I am playing in single player, so no other interactions with the loader than by myself.

here's the save file.

https://we.tl/t-msYQxwYx3n

This is perplexing. The error shown doesn't seem to be possible with the save you sent me. Is it still happening?

It turns out it crashes whenever I load a creative mode "test" map. During regular sandbox play it doesn't crash. Never tried it in sandbox. Wonder why it crashes on test maps tho.

edit: yes, it still crashes in creative mode during Version: 0.7.5

I'm sorry, I am not finding a reproduction. When you say a creative mode "test" map. Is that hitting Ctrl-Alt-E from Editor Extensions, or is it loading a new game with the Editor Extensions Test scenario? Is it a different save? Is it the Creative Mod? The Sandbox mod? Some other mod? I really need some specific steps or a video on how you're reproducing this with an exact list of mods loaded when it happens.

My fault for thinking Testing scenario is vanilla. I use https://mods.factorio.com/mod/EditorExtensions

With the mod EditorExtensions enabled I picked:
Map Editor -> New scenario -> Mod scenarios: Editor Extensions/Testing.

So here's the crazy thing now. If I start a new Editor Extensions/Testing scenario the loaders don't crash on me anymore.
If I play on the older scenario that I have running it crashes.

I'll try and see if I can record it later.