Factorio Forums

on load, it states there's only 1 electric furnace reported on the pollution screen even though 3 are running. pollution is 3/m which indicates 3 furnaces.
at ~ 1:16:40 pollution and count of electric furnaces goes haywire and pollution turns to y/m which instantly changes evo to 1.0 . save is from 1:14:00ish. Based on some testing, the scenario modified pollution diffusion > 5000% which seems to be when this behavior starts.

There are two bugs here, so I will address them separately.

Pollution statistics showing "1" on the icon when there are 3 furnaces - Not a bug
The number shown on the icon is not the number of polluters (or pollution consumers for the right graph), but the amount of pollution they accounted for in the shown timeframe. At 3 pollution per minute and a 5 second scale, the total amount of pollution is 0.25, which gets rounded up to 1 so we don't show a 0. If you use larger time scales you'll see larger values on the icon as well.

Pollution going "haywire" - Won't fix
You are right, the pollution diffusion of >5000% is the cause for the weird behavior. Diffusion settings beyond 100% cause the calculations to produce unintended pollution values, which then compound over time. The weird numbers you see on the pollution screen at ~1:16:40 are caused by these compounded values reaching back to a chunk with a furnace in it, creating inaccuracies because of the huge values at play.
To prevent this sort of behavior, please try to keep the diffusion factor in the recommended range of 0-25%.
As a side note, these strange pollution values are what will flag the save you posted as 'corrupted' from 1.1.54 onwards, due to 101654.