If you have tables in a Word doc or Outlook message and you suddenly can’t see or click on specific cells, chances are good that 1) the tables have merged cells, 2) you’re using Word 2016 or Outlook 2016, and 3) you installed this month’s KB 3213656. The buggy patch was pushed out the Automatic Update chute on Aug. 8.
Microsoft hasn’t yet acknowledged the problem, but there are several credible, detailed reports about the bug. The only solution is to uninstall KB 3213656.
Poster RAJasonCampbell on the Microsoft Answers forum describes the bug thusly: