Open Finder, do Go → Go to Folder…, enter this value exactly, the ~ is important - it refers to your user home folder:
~/Library/Preferences/
you should be able to locate com.blokas.midihub-editor.plist there.
Or you may run this command in a terminal:
rm ~/Library/Preferences/com.blokas.midihub-editor.plist
We’d appreciate if anyone could send us the com.blokas.midihub-editor.plist file before deleting it, so we may reproduce the issue on our computers, and hopefully get the editor to sort itself out from such a state. 