Hi,
I had issues with VCA groups when we bought our refurbished console from a Spanish consoles seller. The VCA fader buss card (CF82E38) had lot of mods made by them.
I would check the CF82E38 card tracks, ensuring that there is not made any track cut or there is not soldered any jumper on it. I would also check 82E20 card, ensuring that all the ICs are working fine and there is not any mod made. Then, you can start finding the issue from the begining.
I say this, because in my case, the tech who own console refurbishing company (Neve, SSL, TAC...), had made lot of wrong mods in different parts of the console. We spende months restoing all the mods and fixing the issues, as they should be fixed.
Oihan