haven't tried a GER game but some observations from my JAP game:
germany seems to be having trouble launching barbarossa in 41, this happened in a few games, GER declares war on YUG(and later Greece) around april/may'41 and isn't done in time for a june barbarossa launch and so the AI waits a full year to declare war on the USSR.
I have the same with 2 games as US; Germany simply does not attack because it is still engaged in Yugoslavia and/or Greece. In one game they finally attacked in 43, the other they declared war on SU in 42.
In earlier versions of AOD/CORE Germany invaded Yugoslavia once it had its troops deployed at the border; sometimes as early as november 1940. In the current version it seems the window between annexing Greece/Yugo and preparing for Barbarossa is a bit small; some stacks are still loitering around Leipzig in june 41.