I've been having problems with ground combat since the new DLC, Dark Matter, came out. I have to pound the hell out of the enemy and they still keep getting more units every turn. The A.I. keeps getting units and my troops keep growing every turn without reinforcements. It took me 25 turns to kill ground forces on a planet of Vodyani. They were at zero population on the planet and no ships were able to get to the system to offload troops, yet their number kept growing every turn.
Could you look into this? Hopefully someone already caught this and told you about it and a patch is coming for the issue.