I think it is an issue with how SteamVR reads the Neo 3 Pro's inputs. Looking at the SteamVR Controller test, there are issues with the Grip and Triggers.
Trigger Axis doesn't work at all, it is either 0 or 1 and pressing about 10% of the way makes it go from 0 to 1 immediately.
Trigger Action is pressed about 11% of the way in.
Grip Axis works fine.
Grip Action triggers when only pressed 5% of the way in.
I'm not sure what you mean by "without UE4 VR Preview"? If I want to play my game without having to constantly build it, VR Preview is the only way. Since Axis Grip readings work, I'll just use that instead of action readings while in the editor.