Different numbers coming from Cloudflare, Smartlook, and Vercel analytics

Question

Over the last four months, I have used Smartlook (by Cisco) for analytics and Cloudflare for security. I started using Vercel analytics yesterday. I have only added Vercel analytics to my web app; it has not been deployed to mobile yet.

• Cloudflare told me I had 128 unique visitors yesterday.
• Vercel told me I had 22 unique visitors yesterday (web only.)
• Smartlook told me I had 2 unique visitors on the web and 6 unique visitors on mobile.

What might be causing this discrepancy? These are all wildly different numbers, and they will determine how many precautions I take when rolling out new features.

Up until today, I have been primarily trusting Smartlook and being rather risky in my deployment practices (no need to be super cautious when you have 8 visitors a day).