Take this advice with a large pinch of salt. I only ever play against the AI due to time/response/availability issues. So I'm aware things are very different playing against a human.
The three things I notice are:
1. The presence of low quality (German) commanders. I've seen several in battle reports that have only 5 Inf rating, with no more than 6 Morale rating and also low admin. I guess you have other uses for Admin points, but I make leader replacement quite a high priority until I have at least 6Inf/6Mor everywhere, preferably 7s with one rating, or with also at least 6 Admin. In every German combat corps at least. I saw Jodl commanding one attack, he's a 3/3 Mech/Inf!
2. There often seems an enormous CC jumble, with units from multiple Armies interspersed thoroughly. I''m sure you are being careful about HQ proximity etc, but maybe that is having some effect?
3. I notice a lot of 'white' units. Which means they are not attached to any army, at best to an army group or even OKH. While there can be overloading problems, I find it makes a big difference getting these attached somewhere.
As I said, I only play against the AI, so this advice may be already well understood, or not entirely relevant. But those things stood out for me.