Two things come to mind:

1. You got the arrows off of ebay so you should probably check tolerances on those arrows. They may have been weeded out as inferior arrows and were accordingly being sold. Do you have any way to check them?

2. You don't just switch from aluminums to ACCs and expect both of them to group with the same setup. If you changed setups did you papertune or grouptune or what was your tuning method for getting your ACCs to shoot right?