I believe this is a server-side issue, and it appears to affect only some users. I am not sure whether it is related to the recent Outlook/Exchange incident. That incident has already been cleared, but as many users here have reported, some people are still experiencing this issue regardless of their language or locale.
The most effective way to make the engineering team aware of the problem is to submit feedback directly from Outlook.com.
In Outlook.com, go to Help > Feedback > Report a problem.
Provide as much information as possible. You can also include screenshots or a screen recording showing the issue.
I also recommend selecting "Yes" when asked whether diagnostic logs can be shared. These logs contain diagnostic information and can be very helpful to the engineering team when investigating the problem.
