Blocked Logged in User from adding remaining items to their cart

I had a wholesale customer who was placing a large order and so was adding a number of items to her cart. She could not place the last 3 items she wanted in her cart. She saw the following message on her screen:

CleanTalk Spam Protection.

Forbidden. Data Submitted Too Often. Please wait a few minutes.

Obviously, this is highly undesirable for my sales and my customer user experience.

What can I do to make sure this doesn’t happen to anyone else? Can you tell me what triggered this? Anyway that you can check if it has been happening to any of my other customers?

Thanks.

Susan