Description of problem:
the dns for *.apps in Google Cloud DNS is not updated when updating ingresscontroller spec.endpointPublishingStrategy.loadBalancer.scope from Internal to External and/or vice versa. 

Version-Release number of selected component (if applicable):
4.7.0-0.nightly-2020-11-18-203317

How reproducible:
100%

Steps to Reproduce:
1. launch a cluster on GCP.
2. change the spec.endpointPublishingStrategy.loadBalancer.scope to Internal
   #oc -n openshift-ingress-operator edit ingresscontroller/default

3. change back the scope from Internal to External
   # oc -n openshift-ingress-operator patch ingresscontroller/default -p '{"spec":{"endpointPublishingStrategy":{"loadBalancer":{"scope":"External"}}}}' --type=merge

Actual results:
Checked Google Cloud DNS and it always shows the first IP 35.202.177.208 for *.apps.<cluster-name>.<domain>.

step1:
# oc -n openshift-ingress get svc
NAME                      TYPE           CLUSTER-IP     EXTERNAL-IP      PORT(S)                      AGE
router-default            LoadBalancer   172.30.33.31   35.202.177.208   80:32225/TCP,443:32658/TCP   5m50s

step2:
# oc -n openshift-ingress get svc
NAME                      TYPE           CLUSTER-IP     EXTERNAL-IP   PORT(S)                      AGE
router-default            LoadBalancer   172.30.33.31   10.0.32.5     80:32225/TCP,443:32658/TCP   6m46s

step3:
# oc -n openshift-ingress get svc
NAME                      TYPE           CLUSTER-IP     EXTERNAL-IP    PORT(S)                      AGE
router-default            LoadBalancer   172.30.33.31   34.72.136.74   80:32225/TCP,443:32658/TCP   28m

Expected results:
step2: the DNS for *.apps should be updated to 10.0.32.5 
step3: the DNS for *.apps should be updated to 34.72.136.74

Additional info:
no this issue on AWS/Azure.