In a new support document, Apple has acknowledged that five limited edition awards may be temporarily unavailable in the Activity app after updating to iOS 12, presumably due to a minor software bug of some kind.
- Thanksgiving Day Challenge 2016
- Mother's Day Challenge 2017
- Veterans Day Challenge 2017
- Thanksgiving Day Challenge 2017
- China National Fitness Day 2018
MacRumors has been affected by this issue on at least one of our iPhones, with a few awards missing on both iOS 12 and the first beta of iOS 12.1, seeded to registered Apple developers earlier today. There's a chance the awards could be restored in a subsequent beta version of iOS 12.1 in the days to come.
Of note, the Mother's Day Challenge award was still visible on another one of our iPhones running Monday's publicly released version of iOS 12, so it appears that not everyone is affected to begin with.