Selective Browsing and Games Stuck at the Loading Screen

Yesterday, I tried to access the NBA website in order to check on updates with regards to the 2016 NBA Finals between the Golden State Warriors and the Cleveland Cavaliers. But for some reason, the site would not load. I quickly checked on Google, and it loaded immediately. Tried Facebook, and it was fine, too. So I thought that it was just a problem with the NBA website.

But then, I tried to go to CNN, and it, too, would not load. I tried YouTube, an videos were playing fine, but when I tried another different site, it would not load. I then knew I was dealing with a Selective Browsing issue. And I knew it wasn't my hosts file causing the problem because I usually edit this only to prevent unwanted pop-ups from advertisement sites.

This issue was happening on both my PC and my mobile phone. On the phone, Viber would not work and some of the games like Clash of Clans and Boom Beach were stuck at the loading screen. FFRK was alright, but another game was not.

So instead of reformatting my PC and resetting my phone back to factory settings, I decided to call up my Internet Service Provider. I already experienced this issue before, and they were able to resolve it by a procedure called port resetting. That was done after an onsite was able to rule out any possible problems with their hardware (modem, filter) and the phone line. All the tech did was call up their support division which conducted the procedure. I asked him what was being done, and his explanation was that my ISP was issuing me another port. ^_^ I guess you can think of it as a water pipe from the service provider that has gone bad (slightly clogged, where you can still get some water, but not all of it), and all they are doing is issuing me another water pipe so that water (information) can flow fully.

I am curious on how the Selective Browsing issue actually happens. In the above analogy, I'd like to know what causes the clogging. There are some explanations that involve an analogy of the browser cache and how this needs to be cleared, and how an ISP needs to do the same thing, but it's still to vague for me. I've tried to search the Internet for more articles on this issue, but have not found one with a satisfactory explanation on the causes and resolutions of Selective Browsing. If you're reading this, and you can explain how it happens, or point me to a resource that has a good explanation, please feel free to post in the comments section below. Thank you.