403 Forbidden blocking my personal websites

... I'm getting 403 Forbidden screens when accessing my two personal websites. I can view them normally with a mobile device using its cell connection, and other ISP's. ...

That means your webhost is blocking your public Comcast IP. You can look up your IP at https://www.google.com/search?q=what+is+my+IP. You'll need to ask the site's admins for help with this.

What does a trace to one of the sites show? In Windows, open a Command Prompt window, and enter

    tracert -4 sitename

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

... they say there is no blacklisting for my IP address ...

I can reach both sites using my Comcast Internet connection, so the block is not a Comcast block. If you are only blocked using your Comcast connection then the host is blocking your Comcast IP, whether they know it or not, and whether they admit it or not. "403 Forbidden" responses come from the target system, not from your ISP or anyone along the path to the target system. Lean on them!

And again:

When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.

I have a very similar problem to the problem described above.

I occasionally receive 403 Forbidden errors on my personal web site at https://www.schweich.com and https://www.schweich.net  

They are hosted by Network Solutions. Network Solutions says they are not forbidding access to my web site. 

I notice the 403 Forbidden errors maybe once a week and the problem persists for a half-hour to 12 hours.

The usual things, like try another browser, delete cookies, re-boot everything, etc., has no beneficial effect.  I have even unscrewed the coax and re-attached it, as requested once by Xfinity support.  

This occurred when I had an old Comcast router, and continues with the new router that I upgraded to about a month ago. 

Ping and tracert to my web site work just fine.  I can FTP into my website just fine, which suggests no one is actually blocking my  IP address or my web server's IP address.

403 Forbidden occurs on my desktop that is connected to my router with an Ethernet cable and my phone that is connected with home WiFi.

If I switch my phone from my home WiFi to xfinitywifi (i.e., use a publicly available WiFi rather than my home network WiFI) I do not get the 403 Forbidden.

If I turn off WiFi on my phone and use the Verizon cellular network, I do not get the 403  Forbidden error.  

The two tests above suggest the problem is somewhere between my desktop and wherever my home network and xfinitywifi come together.  This is an Xfinity problem, most likely at my router. 

I've been on the phone Xfinity support for hours while they diddle, and often the 403 Forbidden error will go away while I am on the phone with them, but no one seems to know what fixed it ... or even if anything they did fixed it.  

I reported an issue through https://spa.xfinity.com/advanced-security  However, that seems to apply only if I have Xfi Advanced Security turned on for my router.   According to the Xfinity app on my phone, Xfi Advanced Security is not enabled on my router.

Any more ideas???

... If I switch my phone from my home WiFi to xfinitywifi ...

If I turn off WiFi on my phone and use the Verizon cellular network ...

In both those cases your public IP changes (see https://www.google.com/search?q=What+is+my+IP) and the host sees the traffic coming from a different IP then the one they see when you are using your home Xfinity Internet service.

"Forbidden" means the host is blocking your Xfinity Internet public IP, whether they know it or not, and whether they admit it or not. These protection systems are often automatic, not well known, and not well understood.

Please be aware that there are 2 kinds of responses in this Forum: Replies and Comments. When you Comment on a post by scrolling down to "Comment on this post here...", I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your response.