Anyone see anything wrong with this 3-way setup

So I’m wiring some 3-ways (GE z-wave plus add-on switch) and its been a while since I’ve taken a class in electricity. Does anyone see anything dangerous with the below?

Basically I have a hot into the light fixture, which leaves me no neutral for the load switch, but I have a switch off a different circuit with a neutral in the add-on box. So I’ve used the neutral in the add-on box for the other circuit for the add-on switch and shunted the neutral from the add-on box over to load box (on the neutral wire) in the 14/3 wire running from the add-on box to the load box. (The black wire in the 14/3 is capped on both ends as I’m only using the traveller/neutral.)

It works, but the neutral for the switch (but not the load) is coming off a different circuit. Anything dangerous with this? What if the breaker was thrown for the other circuit…the switch may not work but no fire hazard?

Edit: After reading some more it seems that a common neutral could cause an electrocution hazard if the first circuit is opened and the second is under load. But in my setup the only load crossing circuits are the z-wave switches themselves… Anyone know how much amperage the switch itself draws?

(On another note, I located a neutral wire wired to a GROUND wire in one box. WTH. Not a bootleg ground…actually using the ground as the neutral despite there being a neutral in the box…)

It’s depend on where this neutral is from. Is the neutral on the same phase circuit? Meaning if you put your volt meter on the line hot of both circuits and it’s 220 volts. Then they are on opossite phase so it should not overload your circuit. Check your local code.
If measuring between both line hot is 0v then it’s a fire Hazard even if the z-wave switch draws no current today. In worst case and If there is an impending short of the Zwave switch. Your neutral could be overload.
Since you have neutral and line hot of a circuit nearby. Why not disconnect both line and neutral and move both to the new circuit? Unless it’s a can light fixture and you have no access?
I see people using ground as neutral all the time. I also spent many days fixing wiring because of this as well.