Hello! Sorry to trouble you guys. However, I recently experienced this problem where I was unable to log into my account. One of my characters' name is Buttermelt. They stated that my account is already logged in, if not, the server is under maintenance/check. This problem persisted for quite some time. I am not logged in from anywhere. I even logged out from this webpage and tried, however, to no avail. (Refer to screenshot above) Thank you!
Log into the control panel in the website and click on the "Character Fixes" option. Alternatively, wait for awhile and you'll be automatically "disconnected".