The Belt Visualizer mod (2.0.2) caused an unavoidable error. Please report this error to the mod's author.
Error while running event belt-visualizer::on_tick (ID O) real number expected got table.
stack traceback:
[C]: in function 'draw_line'
＿belt-visualizer＿/scripts/rendering.lua:32: in function 'dash'
＿belt-visualizer＿/scripts/highlight.lua:221: in function '?'
belt-visualizer＿/control.lua:338: in function
＿belt-visualizer__/control.lua:306>

I got this exact same error today when placing yellow "corner" belts to connect red & yellow underground ghost belts together. This hasn't happened before with many hours of use and I had a recent auto-save so it didn't worry me much, but I figured I'd report it at least. Hope this helps.

I was able to replicate this error - it happens consistently if I place a yellow underground belt, queue it to be upgraded, then queue a red underground belt to be placed where it'll connect, but one tile beyond the max range of a yellow underground belt. Then, clicking the belt visualizer hotkey on the red underground belt ghost causes it to crash every time.