Hi riesta kristianti tannia,
The EncryptPassword action may be using the username as part of the hashed password (check here to see how it is implemented in the Users module). In order to have that behavior enabled, someone would have had to modify the value of site property IncludeUsernameInPasswordHash in the Users module.
If that's the case, it is possible that passwords stored before this change are not using the username, whereas passwords created afterwards (and the validation mechanism) are using the username as part of the text to hash and store in the database. Also, if you changed the username, that might not have been used to change the password hash, which means it will always fail (as the new username + original password will generate a different hash from what was stored).
Can you try creating a new user and see if that one can log in easily? Also, can you open Service Center and check what value does the site property IncludeUsernameInPasswordHash in module Users have.
Cheers!