I have seen the same issue. The explanation was that while my server was switched off the expiry date for the jobs relating to the recurring sets had passed.
Jobs are set to expire after two days.
As a result those sets are never executed again. The next execution date is read from the Hash table but the data in it is never updated because there is no job to run.
The reason I experienced this is that my application is in development so is only running stop/start in IIS Express. Its mostly not running especially over the weekend!
Its a pity that we don’t have the option to specify expiry time limit.