Ideas
I have similar problem in my save.
it is just a single gnome at a time, but 1 every day for a few hours, and many green pulse spots.
its not every lot.
I do have mods (will check with out later)
It seem the gnomes might be coming to lots with decorative gnomes? becouse first house it happent in defently had 1 gnome in it (Specter in Ravenwood) Im not sure about the second but does it havnt happent I dont belive had any decorative gnomes.
I have not seen it happen on community lots.
No ailments (on my sims and really if walk by sims make it happen it is bad, though didnt see any walk by with ailment)
and I didnt use fairy dust.
just 1 gnome do its thing for like 3? sim hours then become statue.... next day or a few days later new gnome pop up.
edit. yes happen with no mod
and yes if destructive gnomes break things I cant allways fix it or it might take 4 tries