Open Stuck on "Testing registration on Join's server..." with Yandex Browser

I'm having a similar problem to the user who posted this thread: https://forum.joaoapps.com/index.ph...n-on-vivaldi-browser-standalone-install.38704

...only, in my case, I'm using Yandex Browser, which is also based on Chrome and also supports Chrome plugins. The plugin installs OK and opens. But, when I run the diagnostics, it just hangs on that "Testing registration on Join's server..." message:



I've also navigated to chrome://gcm-internals/ as you recommended the other user to do, where I see this [for contrast, I've also included what I see in Chrome as well, where the plugin does work properly].

Yandex Browser:




As you can see, there's a "Socket_Failure" error showing up there. But I've no idea how to resolve this.

With Chrome Browser:




Oddly, if I navigate to https://joinjoaomgcd.appspot.com. Again, as you advised the other user, I just get a blank page using both Chrome and Yandex, even with all other extensions which might affect the connection disabled [uMatrix, HTTPS Everywhere and uBlock Origin]

Yandex Browser: a blank page



Chrome Browser: a blank page and an alert about not bering authenticated. Even if I click the alert and successfully sign into my Google account on the window which opens up next, the 'Not authenticated' alert just pops up again afterwards and I still get a blank page.



However. In spite of these errors on Chrome, the plugin does work:



It's only on Yandex that I can neither get the plugin to work OR the web app.

Would love to get this working on Yandex, as I use it as my default browser instead of Chrome and, in theory, it should work, seeing as Yandex supports Chrome plugins. Any ideas what to try, to resolve this?