I’m getting the impression DESS tries to minimize discharge. It accepts wasting solar gains that exceed prediction.
Look at my system below. It stopped discharging at night and started buying. Presumably because it thought it couldn’t fully recharge during the day.
Predictions being unreliable as they are, it would be smart to allow full discharge. If you were even smarter, introduce a gambling factor (the odds that forecast is wrong).
Witch mode are you using, green or trade?