The Russians sacrificed a good chunk of their maneuver capabilities in the attacks on Kiev and Karkov. They have major problems with logistics, training/troop quality, and equipment. They aren’t getting near Odessa in the near future, if ever.
The Russian military officers and intelligence agents all lied to Putin. So Putin thought that his military was ready to go because it is completely modernized. Well, in a sense, they are able to beat a lesser foe like ISIS in Syria but not an advanced 2nd world nation (with arms from 1st world allies).