I just did it two days ago with absolutely no issue. It looks like from the quote you added that it is an issue on Xfinity's end for some customers. So far, it seems like I'm not one of them. Hopefully it will stay that way.
It also looks like a lot of the people in the other thread may be using a docker image. I'm not. IDK if that would make a difference and if it did why, but maybe that's a possibility.
The container is using Chromium 89. The current version of Chromium/Chrome is 96. That may be an issue, but it could also be a red herring.
I am not using docker
If I’ve gleaned the naming convention correctly, it’s…
DS(DiskStation)2(# of bays)20(model release year)+(Intel processor)
You gleaned correctly, except for 2(# of bays) because that is actually maximum bays (including expansion).
My DS1513+ and DS1019+ only hold 5 drives, but are expandable with an expansion unit.