It’s a response to “End Cheer Leaking” idea posted by one of the developers:

Cheers quotas
We’re going to keep playing around with the way cheers are awarded but currently you “earn” a bonus cheer for each cheer that you receive. But your daily base quota and “earned” cheers work on a 24-hour rolling window, so your allotment can change at any time. For instance, your scenario probably arose because you’d spent your base quota of cheers for the day, but had “earned” two bonus cheers within the last 24 hours. Then those bonus cheers expired. Make sense? We could make this more transparent but we are likely to keep tweaking the system…and their mystery is part of the appeal of cheers, no? ;-)