Thanks. As I expected.
The way those switches are wired violate the NEC or whatever code you’re subject to and most importantly, present a real safety issue. But I have a solution to get you out of this mess.
I’ll explain the problem first:
You do in fact have a line and load in separate boxes, as you first suspected. When you have a line and load in separate boxes, the power originates in one box and is sent switched to the other box, which then routes the switch hot to the light(s).
In your case, the line (comprised of a hot and neutral) originate in the box with the dumb switch. You can see the pigtail from the black (hot) bundle to the black screw of the dumb switch. The neutrals are bundled and tucked into the back of the box.
When you wire this properly, you need a 3-wire (not counting the ground) between the two switch boxes. The way it works is that you need two conductors for travelers and a third conductor to send the neutral. That load box needs a neutral because the load box has to send the neutral to the light.
In your case, you only have a 2-wire between the switch boxes, not the required 3-wire. So there is no neutral in that far box. The very improper solution: Attached the neutral conductor going to the light to the ground. So when you removed the white conductor going to the light from the ground, the lights no longer work.
Doing that is extremely dangerous and for that reason, the NEC prohibits it. It can result in a fire and shock hazard if something goes wrong, because the safety mechanisms have been circumvented.
I did a quick AI query to get a succinct summary:
“Using ground wire as a neutral in a switch box is extremely dangerous and can lead to severe electrical hazards. The ground wire is not designed to carry the return current of a circuit, and it’s crucial for safety, as it provides a path for fault currents to flow to the panel and trip the breaker, protecting people and equipment. If ground wire is used as neutral, it can become hot and cause shocks, overheating, and even fire hazards.” Results from a “what is the danger of wiring using a ground as a neutral in a switch box” search.
I’ll post a potential solution next.
