The NAT address pool does not support multiplexing QinQ sub-interface addresses. Change the sub-interface to vlan-type dot1q.
For example:
#
interface GigabitEthernet0/1/0.1
vlan-type dot1q 124
ip address xx.xx.253.242 255.255.255.252
#
[NE20E-nat-instance-nat1-nat-address-group-address-group1]section 0 unnumbered interface GigabitEthernet0/1/0.1
[*NE20E-nat-instance-nat1-nat-address-group-address-group1]commit
[NE20E-nat-instance-nat1-nat-address-group-address-group1]display this
#
nat instance nat1 id 1
service-instance-group group1
nat address-group address-group1 group-id 1
section 0 unnumbered interface GigabitEthernet0/1/0.1
#
Hope to help you!