The login works on the app but not online

For some reason a while ago I created a musescore account on my iPad(in the app). I used it for a few months then decided it would be helpful if I could use it online too. I knew my login and put in the login details it then came up saying it was wrong. Then I used my iPhone and the musescore app to try and slowly put in the passwords I sometimes used on different account(not associated with musescore) and hopefully try and find what my password was. I then used my login details which I had already used to log in online and it worked.i have also made a new one to test out this and this one to send in the issue.
To try it yourself.
1) download the musescore app then create a new account with your email(not google, apple or facebook).then note down the password

2) try logging in with your new account with your username and the password you noted down