Problems getting GE Smart Switch and AUX switches to work properly

Almost all smart switches require neutrals. There are a few exceptions. Several early Z-Wave devices did not require neutrals but they also do not support LEDs. As far as I know, the only two that do support LEDs are Lutron Caseta (which requires a second hub) and a new switch by Leviton (which seems extremely difficult to find).

Otherwise you need a neutral. As stated above, I highly recommend this FAQ for 3-way switch wiring.