thank you so much for your response! 
@tom.abin789 i think you are using extension, vpn or firewall which is blocking your request please disable them and try again.
@riteshchoudhary2605 I am sorry but that didn’t work, unfortunately. Plus with the same browser and network configuration, it worked smoothly up until two weeks ago.
Hi @riteshchoudhary2605 the problem is as you said. It is the network that is creating the issue. I just realized my work-ip is banned by katacoda.And that was creating all these issues. Thanks for your help and support @rahul456 as well.