Attach Notes 0.4.0 causes a non-recoverable error when it is used with AAI Programmable Vehicles 0.6.10 in base mod: 0.18.34.
When closing a GUI after selecting a figure for showing on the signpost, if you were selecting a virtual signal of a vehicle in signals tab (not logistics tab), AI Car ID for example, the mod fails at line 500 in scripts/entity-notes/gui-templates.lua with message of "Unknown sprite "item/car-vehicle-machine-gun-_-signal". Sometimes it will not fail immediately, but if you put a mouse cursor on the signpost, it will fail.
You will also notice that the icon is not showing on the signpost when you change the icon in the GUI. The mod usually updates the icon which is shown on the signpost immediately, but for the icons which fails, the icon shown on the signpost is blank.
As the icon itself is shown correctly except the signposts on the field, I think the icon data itself have no problem.
Maybe this is somewhat related to information written in https://lua-api.factorio.com/latest/Concepts.html#SpritePath
"SpritePath: It is specified by string. It can be either the name of a sprite prototype defined in the data phase or a path in form "type/name"."
In gui-templates.lua, path is hard-coded as "item/". The type of the icon which caused the issue was "virtual-signal".