This article provides a solution for when the page cache is warming up and fails with an error:
ERROR: Warming up failed:
Cache warm-up failing.
Steps to reproduce:
Start cache warm-up operations.
Pages or whole site loads.
The site is unavailable or the response time is too high. ERROR: Warming up failed:
Cache warm-up doesn’t work with HTTP access control enabled.
Ensure that you do not have access control enabled: go to the specific branch/environment and click on the Settings icon, and check the HTTP access control setting - cache warm-up cannot occur in this scenario, and access control has to be disabled.