Try turning down the softness a bit, and you will get less “banding”. Also try connecting the two walls, or extending the small one back to reduce the “light leaks” between the objects. you might want to adjust your bias also if the shadow under the plant does not show up.
If in 2.8 try using the eevee engine as render engine, then shadows will be affected by blenders own shadow settings for sun lamps for instance (se attached image). Havent tested Exponent and Bleed bias yet myself, but softness and bias should help you tune the problem i would think, also try the different “Map Side” settings in the Verge3D settings in render tab.
Hopefully somone else can chime in if i missed somthing or if you got furter problems.
This reply was modified 1 week, 5 days ago by elk.