Wait. Since posting the above comment something struck me:
AUTHENTICATE failed. 113 consecutive errors.
That sounds like 113 consecutive attempts to access the IMAP server within a short period of time.
Does that make sense to you? Did you keep hammering the server with test emails? Or did you have dozens or perhaps hundreds of active agents and / or users generating emails at that time?
Because otherwise it almost sounds like it could be a security issue. Like a spam bot trying to use your installation, for example.