Originally posted by Alexander The Great:

Hello there. First of all, I would like to thank you very much for making such a beautiful mod. My problem is that NPCs and vehicles sometimes disappear. When I check their properties, I see that “Visibility” is not ticked. Even if I tick it, they don't become visible. I found it very interesting. Is there a setting?

When you say check their properties, do you mean using the zeus enhanced mod?
Please give me more information about how are you playing, multiplayer? Are you zeus for a group?

If I'm assuming correctly, that visibility atribute actually determines if the unit will be able to see enemy unit, it does't make the unit itself invisible or not, the reason it's unchecked and units are going invisibile sometimes is likely because of the Fog Of War system that I have implemented, this system hides units that are hostile to the zeus player when they are not inside the view of any friendly units.

If you want to ignore this system entirely you just need to go to Addon options and uncheck the option "Enable the new spotting routine".