I believe I have identified this issue. This error occurs when “Use Proxies” is set.
I discovered error initially because I had a template repeater, and the template it was repeating had a web browser component. In the repeater only the first instance of the template would load the web browser content correctly. The remaining templates web browser component would be blank and the error I posted would be displayed.
Through all of this I have been using the Web Browser Component with proxy settings. I have found that when I set “Use Proxies” to false on the Web Browser component, my template repeater works just fine.
I have also found on macOS only, when I interact with resources that include a web browser component, I am very frequently presented with the macOS loading wheel for 1-2 minutes. On occasion, this stretches to 3-5 minutes. Once or twice it has lasted 5-7 minutes. This might be worth looking at as well.