"I'm working now to backport" comment added, but then no PR is created

[vstinner]

The PR python/cpython#20412 had "needs backport to 3.9" label when merged, miss-islington commented "Thanks @tiran for the PR tacotada.. I'm working now to backport this PR to: 3.9." but 10 minutes, no PR was created.

• Second try: I removed/added the label again, nothing
• Christian removed/added the label the 2nd time: nothing

:-(

How can we investigate such issue? Who can help on such issue?

@Mariatta or @ewdurbin: do you have access to the Heroku logs?

[Mariatta]

There was bug in latest celery celery/celery#6153
I've reverted to previous version for now.

[terryjreedy]

And on retry the failed backport worked.