I’m not entirely sure if that is what solved it but once thing I did was clearing the DNS cache (following render.com docs instructions)
But it still is a few stressful minutes. One thing I’d like to suggest which would help, is not hiding the DNS settings from the service custom domains instructions. Once the DNS have been verified by render, the instructions get hidden. That could make sense if all was absolutely resolved, but since there is a delay, I’m left wondering if I truly set them as instructed to, or if I modified them by mistake after the fact.
Leaving them displayed would allow me to double checked this is not what I should check.