Outlook 365 suddenly won't open

This is an interesting read...
https://www.computerworld.com/article/3567096/outlook-went-down-for-four-hours-wednesday-what-happened.html 

Especially the anonymous post that was posted on AskWoody, stating the below. 
So it was no client side issue, there was no faulty patch, and no new patch to install. 

Question is then, what is Microsoft trying to change in regards with client authentication that they are unable to share ANY details about as part of what happened yesterday. To me it feels as if Microsoft is aware of some 0-day critical vulnerability they tried to patch yesterday - unsuccesfully as they had to undo the change - but can't share any details yet as explaining what happened would publicly expose the vulnerability. Just my gut feeling though... could just be a new feature too, but the timing and the way Microsoft is (not) communicating currently about what happened seems odd to say the least. 

Can’t tell you my source but basically rumor is something was pushed server-side on Microsoft’s end in regards to a security or authentication change (who knows what specifically) and in that change it cut off communication with Outlook clients past a certain patch. I confirmed this was not last night’s patch that contained these changes, but one previously issued. I do not know anything more specific about this patch in question. This is why rolling back worked – it went to a client version that was before that change in how it talked to their servers. Why this was done in the middle of the day, I don’t know. Very unusual. All I’m willing to go into right now.