Scheduled reboot that should run every second Sunday, doesn't seem to run on the correct dates/days

As far as I know the second Sunday in August is the 14th. The job seems to have run on the 7th.
Next job is scheduled to run on the 11th of September, which seems to be correct according to the "Run on the Second Sunday" trigger I've setup.

Is there any good explanation why the job ran on the 7th instead of the 14th of August?