@JammyDodger Thanks for your reply.
The block is happening for all the users and yes CDN is enabled infront.
Thanks for all the suggestions.
Well, what I have done is used local hostfile method to point the IP and access the forum. Logged into the dashboard and removed Screened IP of that one user account which was blocked and that resolved the issue. Wondering how come discourse considered that single IP and kept on blocking every user from various IPs from the CDN.
Anyways, now the problem is resolved. Much thanks to you as well as the community.