CBR750 — Orbi WiFi modem/router refuses to connect to a specific domain

I have a strange issue. I have been webmaster for a particular website for years, and have rarely had problems connecting to it.

But over the past few days, I cannot connect to my website (or any other website within the same domain, souheganvalleychorus.org), from any device in my home that is connected to my home router, an Orbi. It simply times out. I have done a traceroute, and that tells me that the request makes it to a Dreamhost server in Portland, Oregon, but then it does nothing more.  I have other websites, and this domain seems to be the only one with this problem.

I've contacted my Internet provider, Comcast/Xfinity, and they found nothing on the router that could explain domain rejection. Dreamhost support tells me that the website is up, and they seem unable to figure out what the problem might be.

I then went elsewhere (my church), to see whether a different internet connection (different modem/router, Wifi), and it connected without any problem. So that convinces me that it's my modem/router.

But I have no idea what to do to fix the problem. 

I have found another entry in this Community that seems to be a similar problem (https://community.netgear.com/t5/Nighthawk-WiFi-Routers/I-can-not-access-one-certain-domain-that-I-need-to/td-p/512140), but the solution doesn't seem to work for my modem/router. I cannot find a way to change the Router Mac Address, as described in the solution there.

Can someone please help me?  Thanks!