1. Verify phasing and field wiring
2. Verify slave A to B wiring
3. Remove VAR load wire from VLX-20. Measure this to ground, and see if it has no voltage or if there is somewhere further on that circuit that is sourcing voltage to load.
If there is line voltage present, investigate field wiring.
If no line voltage is present, investigate possible issue with VLX-20 by replacing board and triac and seeing if it's fixed.