You join the server and everything is perfectly fine. What is the correct course of action?
I can see that this question is asked in the perspective on an administrator. I don't see that this is actually a question or that the question is much to vague. Let me see what you where really trying to ask.
Example: A player has called you to deal with a problem regarding a microphone spammer. You join the server and everything is perfectly fine. What is the correct course of action?
I believe that is what you are asking for. To handle a situation regarding an alert and no issue is detected.
I would also like to ask if you could put a section for any additional questions/comments/concerns regarding administration in addition to the administration forum application review (very last question on the forum).
That you would just wait and see if they start up again, whoever the accused is. If you get complaints about said user, give them a warning or something.