Why do some Forge apps in Confluence or Jira Cloud fail to load and show a spinning wheel?

Issue:

Forge Apps in Confluence Cloud may fail to load, showing a persistent spinning wheel. You may also see an error was loaded over HTTPS, but requested an insecure frame...

Common Cause:

This is often caused by network-level security tools (such as DNS filtering or proxy inspection) blocking or rewriting requests to Atlassian’s content delivery network.

Solution:

Ensure that your network allows access to the following Atlassian domain, which Forge apps use without inspection or modification:

Atlassian maintains an official list of domains and IPs that should be allowed here:
IP addresses and domains for Atlassian cloud apps | Atlassian Support