Issue customer is experiencing:
Despite manually removing the alternate service (old) and saving the configuration from the UI, the alternate service did not get removed from the route, and the changes did not take effect.

From the UI, if using the Form view and select Remove Alternate Service, click save, if they refresh the route information it still shows the route configuration with Alternate service defined.
If they use the YAML view, and remove the entry from there and save it's gone properly.
If they use the CLI and edit the route, and remove the alternate service section, it also works properly.

Tests:

I have tested this scenario in my test cluster with OCP v4.13

• I have created a route with the Alternate Backends:
  ~~~

1. oc describe routes.route.openshift.io
   Name: httpd-example
   Namespace: test-ab
   Created: 5 minutes ago
   Labels: app=httpd-example
   template=httpd-example
   Annotations: openshift.io/generated-by=OpenShiftNewApp
   openshift.io/host.generated=true
   Requested Host: httpd-example-test-ab.apps.shrocp4upi413ovn.lab.upshift.rdu2.redhat.com
   exposed on router default (host router-default.apps.shrocp4upi413ovn.lab.upshift.rdu2.redhat.com) 5 minutes ago
   Path: <none>
   TLS Termination: <none>
   Insecure Policy: <none>
   Endpoint Port: <all endpoint ports>
   Service: httpd-example <-----------
   Weight: 50 (50%).
   Endpoints: <none>
   Service: pod-b. <-----------
   Weight: 50 (50%)
   Endpoints: <none>
   ~~~

• Then I tried deleting it from the Console.

• After removing the Alternate Backend from the console in the Form view, I saved the config.

• But upon checking the route details again in the CLI, I could see the same Alternate Backend even though I have removed it:
  ~~~

1. oc describe routes.route.openshift.io
   Name: httpd-example
   Namespace: test-ab
   Created: 12 minutes ago
   Labels: app=httpd-example
   template=httpd-example
   Annotations: openshift.io/generated-by=OpenShiftNewApp
   openshift.io/host.generated=true
   Requested Host: httpd-example-test-ab.apps.shrocp4upi413ovn.lab.upshift.rdu2.redhat.com
   exposed on router default (host router-default.apps.shrocp4upi413ovn.lab.upshift.rdu2.redhat.com) 12 minutes ago
   Path: <none>
   TLS Termination: <none>
   Insecure Policy: <none>
   Endpoint Port: web
   Service: httpd-example. <-----
   Weight: 100 (66%)
   Endpoints: 10.131.0.148:8080
   Service: pod-b <-----
   Weight: 50 (33%)
   Endpoints: <none>
   ~~~