Time Machine stuck in "backing up" 2016-001 security update.

After the last "security upgrade" 2016-001 (September 4, 2016); OS 10.11.6, my Time Machine is stuck in "backing up" in both, my home (for more than 20 hours now) and office external hard drives. The home backup has a long history and usually requires from TM to delete old backups, the office backup, however, is a new 3 TB HD with just one back up and plenty of free space. Has anyone experienced any problems with Time Machine after the 2016-001 security update? Thanks!