So I turned off the [Infinite armor/tool durability] setting and the [mining-tool (axe) removal] setting (i'm playing with nanobots), and now I get a solid green line across the game screen just above my toolbar. This only happens while I'm in an active game, and not on the title screen or opening menus. The green line does not extend outside of the Factorio window.
I turned the settings back on and the green line went away. After some testing, I found it only happened when the [mining-tool (axe) removal] setting was disabled.
Anyone able to test and see if this happens for them as well?