In the new UI, if you're watching a job complete and it fails for a spurious reason (e.g. connectivity), then you click Rerun in the top right, you cannot "Rerun from start". It's disabled in the menu as shown in the image linked below:
If you refresh the page it becomes enabled. This seems out of keeping with the rest of the page, which updates as the job makes progress.
This was confusing until I realised you need to refresh and is now just a regular pain point using CircleCI.