Ad blocking not working

Working on all devices except 1

URL that populates Ads on working device blocks, same URL on this device, not blocking

Next DNS installed on device

Device is behind added Public IP 

This device uses Forti VPN to connect for work; expect the the Ad blocking  not work when connected to VPN

Suspect somehow the Forti DNS is being cached which is why it is not blocking ads, how do I fix this?