I have a recurring issue with a 2017 Macbook that I, Apple, and Comcast have not been able to solve.
This problem occurs in BOTH Chrome and Safafi and is SPECIFIC to my home Wifi, which is running on a Comcast Gigabit modem/router.
Only some Web sites are accessible. For example, Google, Bing, Yahoo all work. Other random sites (Pinterest, NyPost, Instructure) do not load, giving an ERR_Unreachable message. So, for example, if (in Chrome) I type New York Post, the Google results page comes up. But, the ACTUAL NYPOST.COM site will not load. Usually, there is an exclamation point to the left of the URL saying the site is not secure. Sometimes it says I am offline.
I have three other Macs, an iPad, and FOUR iPhones connected to this Wifi Network and not one of them has this issue. Here's what's been done so far:
1) Unplugged router. Twice. No change.
2) Changed DNS settings on problem computer to match the others that work. No change. Also removed and re-added the network and removed and re-added the location. No change.
3) Tried both 2.5 and 5GHz networks. No change.
4) Cleared browser cache, etc. No change.
5) Set up a new Admin Account in Mac OS. No change.
6) Reinstalled MAC OS. No change. This was happening on High Sierra and continues on Catalina.
I am at a TOTAL loss. I've have two hour-long calls with Apple. Comcast blames Apple.
Again, this computer works on other Wifi networks. Just not my home network.
Other ideas? I'm desperate.
Not sure if you ever resolved your issue, but I've been having this same problem across multiple devices since mid-December. Some devices work absolutely fine, but others (both laptops and mobile phones) refuse to connect to specific websites. I can tell you that the issue doesn't seem to have anything to do with Apple... I have this problem on a 2018 MacBook Pro, a 2019 Dell XPS 13 and my Android phone.
Are you using an Xfinity provided gateway (modem/router combo)? I've been on the phone with Comcast multiple times for several hours but to no avail. As a last resort, I'm considering returning my Xfinity gateway, purchasing a different approved modem/router combo and seeing if that helps.
Let me know if you've already fixed this issue, it would be a huge help for me to figure out the solution!