are you using shielded cable for the SLC,or addressable loop data? Shiners, and shield grounding somewhere out in the network, can cause intermittent ground loops that go away with vibration of a wall where a box is. Sometimes, devices on the network are near water or moisture, and ground fault until the day heats up and the moisture disappears. J-boxes that are crammed with connections can cause a ground fault through capacitive connection.
try pulling the data off the network, and meter both sides of the circuit for resistance. You may sometimes see one side to ground varying steadily,which might be an induced connection to a grounded circuit.
Happy hunting
