Apparently there is still the socket unit check_mk.socket active and listening. That shouldn’t be the case after uninstalling the rpm package. Try to stop and disable that unit:
systemctl disable --now check_mk.socket
You can also run systemctl cat check_mk.socket (or status instead of cat) to see where the unit file is located. Looks like the uninstall procedure of the RPM doesn’t remove that file. Remove it and run systemctl daemon-reload afterwards.