solving equations – Solving no longer works

I have defined four functions

fA(x_,y_):=Sqrt(x^2+(y+2)^2)
fAB(x_,y_):=Sqrt((x-3)^2+(y+1)^2)*Boole((y>=(1/2-(1/2)*x)))+(Sqrt(5)+Sqrt((x-1)^2+(y)^2))*Boole((y<(1/2-(1/2)*x)))
fABC(x_,y_):=Sqrt((x-3)^2+(y-3)^2)*Boole((y>=x))+(2*Sqrt(2)+Sqrt((x-1)^2+(y-1)^2))*Boole((y(1-(3/2)*x)))

Before defining the room, I used Solve and it worked as expected.
However, after defining the room, Solve stopped working, even for functions it previously worked for.

Solve(fA(x,y)==fABC(x,y),y)

Now it gives the error "Solve: Undefined is not a valid variable" and returns

Solve(Undefined,Undefined)

The problem seems to have something to do with the variable y, since Solve still works well with other variables.

Does anyone know what could have gone wrong? Sorry if an equivalent question has already been asked. I couldn't find one.