The way I understand the invasion is that Putin didn't tell anyone, either political or military, what his aim was. The military planning was based on a short conflict, either to the front-lines of the new "republics" or to the boundary of the Donbass. That would have been feasible in 48-72 hours, and food, fuel, ammunition etc sufficient for that was on the border. That seems to be one reason everything has been slowed. Add to those problems the situation where a lot of the younger (conscripted?) troops though they were on exercise, not at war, and you are ripe for desertion, mutiny, internal sabotage.