Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Opus Domini – Apples Digital Leather Planner
In the busy routine of our daily lives, planners have a very important place so that nothing can be missed out what is deemed as important. The new application of the Mac operating system is something close to this agenda and is designed to provide the same comfort level thereby, eliminating the issue of carrying agendas which were not only bulky but were a difficult task to do. The Opus Domini allows the user to monitor the daily schedules along with the option to remember long term tasks as well as being up-to-date with the outside world with the help of an in-built tracker.