I use Firefox by default so I tried three different web browsers on my PC, all with the same result, so it isn't the browser blocking the graphs. Then I used my mobile phone browser over 4G not Wi-Fi, and the graphs are displaying correctly. The web host in the USA confirms there is no problem with their servers or scripts.
Best answer by Igor Kurzin
Does it help to set it to “Do not scan encrypted connections” in Settings → Network settings? Restart browser and check.
If not, does it help to disable “Inject script into web traffic to interact with web pages”? Restart browser to check.