OK, I have not yet tried to move back down to 3.1.1 but since I saw that 3.2.0-beta2 was released I thought I'd try it. Mixed results.
Here's the results with various browsers
Chrome 64 bit 85.0.4183.121
Still does not automatically update the graphic when you click on heightmap. If you manually reload the page you now see the updated map. I no longer get the "cannot read..." error message. So, an improvement.
Firefox 64 bit 71.0
When you click heightmap you see a flash of the graphic and then nothing. If you click on the "invert z coordinates" the map graph is then displayed. You still need to reload the page to see the updated graphic.
Brave 64 bit 1.18.84 Basically the same as Firefox.
Edge 64 bit 85.0.564.68 Basically the same as Chrome
Internet Explorer 64 bit 11.508.19041.0
This is interesting in that it never shows any DWC page. All you see is a blank page.
This is all on Windows Pro version 2004 64 bit with all updates as of this afternoon.
I'll try 3.1 but I don't expect any change.