A high number of unique clicks, mostly occurring at the beginning of a send, can be caused by certain email server security suites that look at tracked links to verify whether a site holds malicious content.
Email security that is shared among email servers you send to, likely uses link checking capability. This is to ensure the sites that are directed to by URLs in an email are not phishing or otherwise nefarious sites that might compromise their network.
Some email security suites have logic that "scan" the links within an email and then uses an automated system to visit that link to verify the nature of the site. Campaign has no way of verifying whether a clicked link is human or machine, so Campaign registers a click whenever a tracked link is accessed.
While not always the case, most email security suites check the email received by the recipient as soon as the mail is delivered. It's often helpful to use RawRecipientDataExport and sort the records in the report by click time to see whether a particular link, or set of links, are quickly accessed in rapid succession.
The same email security suite can be shared among recipients you send to even if they do not share a domain name. For example, if many of your recipients are B2B type contacts who exist on exchange servers, then it's likely the same security suite used by the various servers all flag the same links. The security suites do not share their algorithms with regard to how links are flagged for possible maliciousness, so Acoustic Campaign is unable to advise how to prevent the behavior.
Email security suites that follow the tracked links can exist within the recipient's mail server itself or an IP range that is owned by a cloud security service. It is not possible to separate the computer and human clicks. When the Campaign servers see that a uniquely tracked link is accessed, it automatically generates the event for that recipient.
Note: Enabling SSL at org level and sending domain may give clients a best chance for the reduction of NHI (non-human interactions).