Windows Security pops up: application prompts for outlook credentials

That first diagram [X1 search] is the one that I see every so often when outlook.com decides that my attempted login is suspicious.
- Once it thinks that there is no point trying again & again because the result will always be the same.
- The only solution is to go to MS Account - recent activity and tell them it was me trying to log in.

So I think you should also check MS Account - recent activity to see what outlook.com thinks is happening during these episodes.

Denis