Hiya! I noticed that this happens on latest Factorio update for me (2.0.28):

Failed to load mods: The given sprite rectangle (left_top=0x0, right_bottom=64x64) is outside the actual sprite size (left_top=0x0, right_bottom=84x56).
If this is being used as an icon you may need to define the icon_size property.
See the log file for more information.: base/graphics/icons/shortcut-toolbar/mip/new-copper-wire-x56.png

Happens even after resetting mod settings (after I'd disabled the copper wire tool). I do have a bunch of other mods installed, but this doesn't seem like that'd be an issue here?

Did you check this without other mods?

Yeah I tested this since and it happens even with no other mods installed. Changing the icon size to be 56 does fix this

Fixed this

Awesome, thank you!