Why are visits not showing or matching up with page views or clicks?

AffiliateWP tracks unique visits, so it won't match up to an analytics tool that is tracking page views, visits, sessions, etc. 

To expand on that further as to what we mean by unique -- when an affiliate's link is first used to reach your website where AffiliateWP is installed, a cookie will be created in the visitor's browser. As long as the cookie remains in that browser and is active (that is based on your Cookie Expiration setting in Affiliates → Settings → General), no additional visit entries will be created in Affiliates → Visits. This doesn't mean your affiliate will miss out on earning referrals, since, any purchases or signups (whatever your integration is) made from that browser while the cookie is active will result in a referral created for the affiliate.
One other setting that can affect when a visit is created is Credit Last Referrer, also in Affiliates → Settings → General. This will create visits for unique, distinct affiliate links. So if affiliate 1's link is used, then the same visitor clicks on affiliate 2's link, another visit will be created for affiliate 2. Basically the last affiliate link used wins.
You can easily test both of these scenarios, simply remember to clear out the AffiliateWP browser cookies when needed. This article can show you how to do just that: