Support will have to look at the specific Dashboard metric and Campaign in detail to be sure, but it is probably due to the different way we count clicks in the Dashboard vs. a Campaign.
The Dashboard will show the total clicks for any Contacts including ones that have been deleted from the Contacts database. A Campaign will count only the unique clicks a Contact makes (only the first click on a particular link), and then only for current Contacts in your database.
As an example, I found the Dashboard metric for 59 clicks yesterday in your Dashboard:
You can click on the "59" to see the Contacts in your database that clicked. There are 15 of them.
I don't know if I guessed the right Dashboard metric, but this one will serve for the explanation. The metric is for clicked any link in an email. The first Contact listed has a first name of Owen and when you open his Contact Record you can scroll down to the Contact Log. Emails sent that the Contact has opened or interacted with have a checkmark, and if you click on them in the log you get the number of times that Contact clicked a link ... and he did it four times:
In this case, the combination of people clicking more than one link, or clicking the same link multiple times like Owen did, and the possibility of Contacts being deleted (but still counted in the Dashboard metric) leads to the discrepancy of 59 clicks but only 15 Contacts (still in the database) accounting for those clicks. You can add the Condition "Contact still exists" to the Dashboard metrics to remove counts for those who have been deleted; we count them because to judge the overall conversion rate, etc. on a funnel or it's elements you need to know the total number and not a new net number based on who is still in your data base.