Link to Apicast template should be different for every 3scale release. I see in 2.5 documentation link from 2.3 3scale, see https://access.redhat.com/documentation/en-us/red_hat_3scale_api_management/2.5/html-single/administering_the_api_gateway/?lb_target=preview#creating_custom_apicast_policies and link leads to https://raw.githubusercontent.com/3scale/3scale-amp-openshift-templates/2.3.0.GA/apicast-gateway/apicast.yml and it should be
https://raw.githubusercontent.com/3scale/3scale-amp-openshift-templates/2.5.0.GA/apicast-gateway/apicast.yml

There is also wrong link https://access.redhat.com/documentation/en-us/red_hat_3scale_api_management/2.5/html/deployment_options/apicast-openshift?lb_target=preview#step_2_deploy_apicast_using_the_openshift_template from " Deploy APIcast using the OpenShift template, specifying your customized image:"