Ask Codex to code based on a link to a GitHub issue

According to documentation codex can be given a link to a GitHub issue in a public repo, and it will read that to do it’s work. I find that it does not consistently work. Sometimes it works and sometimes it says something like: “I don’t have network access in the current environment, so I’m unable to view the issue at that link.”

Can anybody advise on how to get it to work consistently?

I found this in an earlier thread Codex unable to find the repo . And it seems that Codex is unable to read a Github issue. I went back to the case where I thought it worked, and I see now that it got the work right by reading the read me, not from the issue.