I experienced this before but after I change my DNS to OpenDNS it solved my issue. If you can access your ISP just change your DNS to 208.67.222.222 and 208.67.220.220
or you can try the google DNS 8.8.8.8 and 8.8.4.4.
If it doesn't work to you switching pool might solve this issue like the suggested above.
changing the DNS will probably solve most blocking issues whether it is mining or something else. i assume most people will do this on a router scale, meaning that whole LAN will be using that DNS, which is pretty risky if you are accessing any type of online wallet, be it on your mobile or a pc. using a public DNS is associated with great risks, tons of coins have been stolen from people who use a public DNS.
read here >
https://bitcointalk.org/index.php?topic=3458297.msg35990380#msg35990380so what you should do is change the dns ONLY on the miner itself from the network tab.