Possibly your Unity project has the wrong colorspace setting. Set project Color Space to Linear to get proper lighting. This is found in Edit->Project Settings->Player. Then click Other Settings tab. Set Color Space->Linear (default is Gamma).
(Follow the various guides around. There are 3 settings that differ from Unity project defaults you need changed for AssetBundles to work correctly in VaM. There is colorspace and two VR related settings.)