False positives CF7

We build websites for a global brand who use a 3rd party agency to test the CF7 enquiry forms from time to time. Each time they test they are getting blocked for malicious activities so the form will not submit and we need to whitelist their IP address for testing. Can anyone explain why this is happening or how I should investigate this? We have lots of other websites using exactly the same plugin as these sites and never have any complaints of forms not being submitted.