Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
"172.19.33.32" is not an "external IP" , i.e., not a Public one
- See : RFC 1918
Can you provide more information on this IP?
- Where exactly does this IP exist?
- Is it associated to a VM in the same VNET or the Peered VNET
OR
A server from OnPremises connected to Azure by VPN or ExpressRoute? - There is a high chance that the IP "172.19.33.32" is not listening in Port 80 to begin with
- How are you confirming that the IP 172.19.33.32 is "still" listening on 80?
- You can use a VM in the same VNET as the AppService and telnet to 172.19.33.32:80 and test this
- If possible, please share a network diagram between your App VNET and the destination "172.19.33.32"
Cheers,
Kapil