Open rates that are 0% may indicate that the connection between Ghost and Mailgun has stalled, which prevents Ghost from fetching your newsletter analytics.
To recover your newsletter analytics, restart Ghost by running
ghost restart from the command line. Restart Ghost as soon as possible because Mailgun logs are only kept for a limited time, after which the logs are no longer recoverable. It’s also best practice to restart Ghost when no newsletters are scheduled to be sent. (If you’re on Ghost(Pro), contact email@example.com for support).
We’re currently working on improving the connection between Ghost and Mailgun so that this issue doesn’t occur in the future.