Managing personal Outlook.com account settings, security, and privacy
This is definitely a glitch and something very wrong with Microsoft's authentication system which they seem reluctant to rectify.
After using this page to login to my email a few times, I encountered the same issue again but this page no longer worked. I left it for a couple of days and was able to log in again through this page and the same problem came back after a while. Extremely frustrated, I tried to seek an alternative method and found that changing the login alias helped.
You may find more details on this Reddit thread that I came across while Googling for a solution: https://www.reddit.com/r/Outlook/comments/yhhlcl/daily_login_attempts_into_my_outlook_email/?rdt=43727
Since I changed my login alias (and ensure I do not use this new alias for anything else), I haven't encountered any more issue with logging in and also noticed there are no longer any unknown attempts of sign-in activities to my email account.
Hope this help you guys who are looking for a better solution. I'm currently in the midst of migrating my primary email to Gmail for a permanent solution since this is not the only issue I encountered with my Hotmail; I've been missing email occasionally and there doesn't seem to be any way around that.