The most common reason when people cannot login and receive message that password incorrect - they are trying to login in wrong place.
For account model
For wallet model
nobody can change your password except you
password is not changing by itself
You can login with ACCOUNT MODEL here https://openledger.io/ with login and password
You can login with WALLET MODEL here https://openledger.io/existing-account with your backup file and password
Please note: if you try to login using correct password in incognito mode ( google chrome) there won't be any issues.