If we run out of suggestions and the next day rolls around, Firefox doesn't know to check for new caps until something triggers it. Existing triggers include restarting Firefox or waiting for the 24hour fetch. This means immediately at midnight, a frequency capped tile isn't shown, but it'll start showing within 24 hours. I don't think this is super critical as the main purpose of frequency capping is to not show it too often, and this bug makes sure it doesn't show too often. This is especially true in a situation where a user hit the frequency cap a few minutes before midnight to then see the uncapped-after-midnight tiles right away. So given that, it might be fine that we have this "bug."
You need to log in before you can comment on or make changes to this bug.