I had the same issue this that site. I think it is caused by ad block. I browse the internet with Firefox that have ad blocking addons installed, but always have Chrome installed without any adddons to test sites just in case. And on chrome it worked OK.

I have Thunderbird opened constantly, so I just open Google Messages in one of the tabs in it. Only problem is that it does not show any notifications, but I get them through KDE Connect.