If a local user is being used, you can change the password or clear it using one of the many rescue CDs / USB boot images such as Trinity, System Rescue, or anything that includes a recent version of CHNTPW.
There are plenty of other password reset disks / utils that work under WinPE like Active@ password changer ($50).
If the forced reboot x3 doesn't open a downgrade scenario, you can try to determine where the password came from.
It's rare that an account becomes password locked without user intervention or a password source.
The following assumes that the account is using a Microsoft Account or Live Account and not local.
"Let me confirm that, if have configured any Windows 10 feature(I.e. Like Xbox, Windows store, Cortana, or any other feature) recently that which requires Microsoft account, then it will automatically switch you to Microsoft account after you enter your account credentials and you need to use the same to access PC. In simple your Local account will be migrated to Microsoft account without any changes to your personal files.
"If you want to switch back to Local account, then navigate to Start/> Settings/>Accounts/>Your Account, on right side click Sign with local account Instead. Enter your Microsoft account password when prompted and follow the steps to switch back Local account.
"But ensure that most of the features on windows 10 require Microsoft account to access them. Refer the link for more information about Microsoft account."
It's possible that you used a MS account with Office 365, OneDrive, OneNote, XBox for Windows...? Maybe the credentials were pulled from there.