Hello
Are you currently logging in with your personal Microsoft account?
Typically you don't need internet connection to sign into Windows because the computer can use already cached credential locally to sign in. If it requires internet, sometimes it can be due to some information has changed, such as password, security info. Or your computer might recently have gone through updates that involves firmware update, etc.
I personal travel a lot and I totally understand the valid concern that you brought up. I would recommend that you always keep a local admin user in the computer. This user comes in handy in so many ways, including the scenario you brought up.
To do that,
- Type netplwiz in the search on the taskbar and hit enter. When launched, click on "Add". On the next window, click on the bottom where it says to create an account without Microsoft email. This will allow you to define your own username. Make sure it doesn't contain space or special character. Set it up as a local user.
- When the above user is created, back to the main netplwiz page, double click on this new user, go to the Group Membership tab, make it administrator. Save the change.