It turns out that a large source of TagBot’s puzzling intermittent failures may be because GitHub doesn’t like to make it easy to tag and release tags on commits that touch GitHub workflow files, and TagBot can’t do so (unless you give it a custom PAT). And GitHub’s errors don’t make it clear that that is why.
When it fails for that reason TagBot should now open an issue on the repo with guidance.
The best way to avoid it is to only release commits (via JuliaRegistrator etc.) that don’t touch workflow files.
The readme has updated info and guidance: