Here are the most probable reasons for this happen:
We detected a tracker that has multiple uses and blocking it would be detrimental to your Internet experience so we decided to let it pass (that action is called whitelisting). That tracker for example may be essential to display a page properly or perform online shopping actions so blocking it would not be worth the inconvenience.
The service provider who provided you with Privowny App decided to make some exceptions.
Our Tracker Filter missed a tracker - New trackers are being created all the time, we’ve indexed thousands of them and are constantly on the lookout for new ones, but sometimes they slip through. We’ll eventually catch them all though.
You already have a VPN installed on your device - Only one VPN can work at a time so, if this is the case, Privowny App usually can detect that another VPN is in the way and will prompt you to deactivate it. Unfortunately, sometimes it can't be detected, so you may want to go and check the settings of your device.