Ok. Have you tryed to move one of this work ok pc, to your new group?
If the answer is Yes, this pc take the policy of new group or not?
If the answer of this question is Yes, you can try to reinstall the Avast client program.
If the answer is No, you can try to reinstall SBC console on server..
Probably reinstall the client is the first thing and fast to do..
Another possibility is to try to remove the PC from the console and then trying to add manually or make a search for new PC in the SBC console.
Unfortunately I've not got another idea to solve this problem! :'(
All my clients respond correctly to any modify on group...