I possibly hit a race condition between the end of the grace period of a bounty and the time the notice is automatically removed.
On Aug 7, 5.08 (everything in UTC in this post) I started a bounty to a question (see revisions or timeline). After seven days it ended and entered in the grace period. By Aug 15, 00.01 I received an email from Stack Overflow:
Your bounty on the question … Paso de B a U: ¿evolución fonética o falta de ortografía? … ended and will be auto-closed after the 24-hour grace period expires.
When I woke up I opened the link on my mobile by around 7 am. The bounty indicator was still next to the unique answer, so I clicked on it. However, it showed a message saying more or less "there is no bounty". Surprised by it, I refreshed the page and found out that the bounty indicator next to the answer was gone. Only later I realized that the grace period was over, so it was correct that I couldn't award anymore.
In any case:
- The email about the grace period was sent at 00.01, which seems to be the standard for bounties (I checked other cases).
- The timeline shows Bounty Ended with no winning answer by Community♦ at Aug 15, 7.02, which is 2 hours after the grace period was over.
- The visual indicator to allow awarding a bounty was still there even after the bounty was over. I cannot recall if the notice below the question was still there.