This counts Change of Authorization failure notifications sent for one specific user group, reporting authorization changes that could not be applied to members of that group. A rising count confined to one group points to a problem specific to how that tier's policy engine references sessions or attributes, rather than a gateway-wide CoA fault affecting every subscriber equally. A group-specific spike right after that group's plan definitions were edited would suggest the new policy references attributes the gateway doesn't recognize for that group's existing sessions.