Electrical help: wired new Z-wave wall switches (fan and lighting), old switches were jumpered and I don't understand the reason
If your gang-box is fed from two separate radial circuits, my understanding is that the neutrals should not be combined but should be kept separate.


You don't want the possibility that the current from two 20A hots can return via one 20A neutral when there is a fault in the other neutral.
You don't want a path by which a circuit can become energised even when the breaker for that circuit is off.
You don't want to trip a future GFCI (or equivalent) installed upstream.