If you have an active WireframeHandleAdornment with too many lines, parts of the CoreGui will no longer be rendered at all. Enough lines will stop CoreGui from being rendered altogether.
Code in any localscript:
local vis = Instance.new('WireframeHandleAdornment', workspace.CurrentCamera)
vis.Adornee = workspace.Terrain
for i = 1, 261200 do
vis:AddLine(Vector3.zero, Vector3.new(math.random(), 2, math.random())*10)
end
Normal Studio:
Rendering 261200 lines:
Rendering 262200 lines:
Kind of goes without saying that after enough lines there will be no more CoreGui rendered anymore.