The problem, at least this time, stems from a failed login on roundcube through DirectAdmin:
"Failed DirectAdmin Roundcube login from 71.193.***.***"
It is likely that has been the case for the previous times too, since it is a temporary block it would be lifted given time and thus restoring access again.
I have removed the block, but please ensure that you are using the correct user/pass combination for roundcube login to prevent it from happening again.