I started a custom campaign after completing the regular campaign but the RTS portions are completely impossible. The most glaring issue is that all the AI forces are involved in every battle, even if they are not present. To compound this problem they don't ever attack each other, only me. On top of that the AI seems to be several notches harder than the 3rd chapter of the campaign, completely abusing the already broken Trooper building capture ability to capture all my buildings in a fashion I can't possibly defend against.

I'm on the latest patch of GoG if that makes a difference.