Environment URL doesn't resolve

Summary

When trying to set environment urls manually or automatically via gitlab-cicd.yaml, a resolvable url (nslookup verified, functionality verified via browser) returns error.

Some urls were functional (http://www.google.com) while some were not (i.e. https://dev.maverick-ops.com/battlemech/index.html), so this may be an issue with our server configuration, though as mentioned above, it does seem that this host should resolve.

Steps to reproduce

Project- Operations - Environments - set URL to https://dev.maverick-ops.com/battlemech/index.html, click save.

What is the current bug behavior?

Cannot save URL error message: "The form contains the following error: External url is blocked: Host cannot be resolved or invalid"

Relevant logs and/or screenshots

Results of GitLab application Check

GitLab EE V 12.2.5

Possible fixes

This issue will likely be resolved with release of 12.3, when dns resolution check will no longer be prerequisite to setting links. Would still be of value to know why the url doesn't resolve in the eyes of GitLab.