I had an issue that caused significant loading times during the 'Loading Sprites' phase in the form of hangups that would last between 3 and 10 minutes. This was revealed to be coupled along side an error in the 'factorio-current.log' file along the lines of;
142.926 Warning! Sprite at {0,0; 32x32} from <mod_name>/graphics/icons/<image_name>.png is defined with 4 mipmap levels, but level 1 is expected to be at {32,0; 16x16} which is out of bounds of the source image.
In an effort to solve this issue I found that adding the line, 'icon_mipmaps = nil' where the icon is declared - adjusted to match the code's variant of declaring it - seemed to fix this issue, at least for me.

Yours is one of the mods I had the error with, and was able to fix using that method so I'm offering that information to you. :)
For this case it was the icons for both furnaces declared in items.lua and entities.lua

Thanks, I haven't played in a while, so I haven't noticed those issues yet.
I'll get on fixing the bug as soon as I find some time, thanks for the detailled info!

No problem! It was a bit of an obscure issue, but after I made a guide on fixing the issue manually, it was expressed to me that I should be letting the mod owners know as well.

Actually, I'd like to apologize if you find this offensive, but I did use your mod specifically as the example for the guide. Not for any particular reason other than it was one of the most recent mods I had altered using that process, and I figured it would be clearer if I used an actual detailed example.

I don't find it offensive at all, but thanks for asking.
I don't have any experience with Lua, and modding factorio is still something I can only do on a surface level, so if I can make something that someone else enjoys, even if it's not the cleanest mod ever, I'm happy.

But I do wanna improve, so if you have suggestions feel free to complain ;)

Fair enough. I'll keep that in mind, thank you. :]

Hi, I've tried replicating your issues, however I am not getting any "Warning" in my factorio log, no crashes, no long loading times. I don't know if it has been fixed by some udpate, but if you're still experiencing the issue, maybe send me the mod list so I can try and reproduce it (although I doubt that any mod can cause a warning in another mod).