Bug happens on 32bit/64bit launcher, with or without mods and every zeus missions, vanillia and user created.
OS: Win 7 x64

Solution is to now include the attribute "side = 8;" in each composition class.

the problem is that now you have to define the side also in the specific group, while its already defined in the upper level

class CfgGroups
    class West
        side = 1;

but now you need also

    class Indep
//        side = 2;
        class IND_F
            class Infantry
                class HAF_InfSquad
                    side = 2;

aka this broke group use for ZEUS in all community mods with cfgGroups definitions (outside A3 vanilla groups itself)

I'm sorry can someone go into more depth on how to fix this issue?

A concrete examples may help. You can use the Ares/Achilles source code as a template.

Essentially the attribute "side = 8" you see in compositions.hpp is the new requirement.

Links:
config.cpp
compositions.hpp
Medium - Op Tower.hpp