Shadow's quality bug? Or just wrong settings?

Hello there, I spent almost 1 week already googling… hope that you can help me with that.
I baked my shadows, result and all needed settings are shown on the picture.
The problem is that quality of shadow on the tree is much much better than of shadow on the ground. Do you have any guesses why?

I just made this one tree bigger than others so that it’s easy to see the problem…

(shadow quality is set as the highest, rendering path is Deffered lightning)

were you able to fix this at all? I am having the same issue!