Scheduled backups stop working, and the following error is listed in the Windows Task Scheduler:
Task Scheduler Error Value: 2147750687 - task already running
Every hour, the Task Scheduler service schedules tasks to be run over the next hour in a schedule window. If the start time of a task coincides with the end of the current schedule window and with the beginning of the next schedule window, then the task may be scheduled two times. In this situation, the task is scheduled at the end of the current schedule window and again at the beginning of the next schedule window.
Steps to solve
See the hotfix by Microsoft.