I don't understand your purpose in adding a new group. It appears that in your network, all the queries to Pi-hole appear to originate from the router IP, so group management is not effective (all your clients are in a single group by default).
I would eliminate the client mapping for the router to the new group, and eliminate the new group. This will apply all your existing blocking to all clients and your Pi-hole will work correctly.
If you do want to be able to apply blocking to individual clients, you will have to make some changes in your network so Pi-hole can see individual IPs. Then, you can put individual IP's in groups.