Scheduling and managing events using Outlook.com calendar
I also just spent hours with chat but I have really good news, I was able to talk to level 3 tech and he acknowledged the problem.
Level 3 tech said:
"yes seems to be a problem"
"I will check it by escalating the case further. Thanks for bringing this to my attention."
"There is no ETA on the fix, however as its global issue so should be resolved soon"
You can see the chat transcript here (all confidential or identifiable information removed):
The Outlook.com team will probably fix the issue pretty soon.