Thanks @deckingman, appreciate your help and gave your suggestions a try this morning. Good to know that M584 returns the drive mapping. I changed the M584 to define all drives every time in config.g and homez.g.
After config.g M584 -> Driver assignments: X0 Y1 Z2:3:4 U3 V4 E5, 3 axes visible
After homez.g M584 -> Driver assignments: X0 Y1 Z2:3:4 U3 V4 E5, 3 axes visible
Behavior is still the same. Running Homez.g the first time after firmware reset and everything works as expected, with the Z, U and V axes rotating the same direction. But when Homez is run a second time, the first G1 Z400 U400 V400 F500 S1 command causes the Z axis to rotate in different direction from U and V. Homez then hangs for a couple of minutes before continuing on with the G1 V-3 F200 S2, and subsequent commands.
Also tried @phaedrux suggestion to enter commands individually from console. Did this after running homez once after reset. Same behavior. Checked drive mapping after the G1 Z400 U400 V400 F500 S1 and it returned Driver assignments: X0 Y1 Z2 U3 V4 E5, 5 axes visible