You can hit ctrl + shift + j to load the error console to see if there are any errors for Twitter. Maybe one of the error messages will reveal something.
In the developer tools, you can switch to the network tab, check "disable cache", and hit ctrl + r to reload the twitter page to test if the network log shows any errors.
Also in the developer tools, you can hit the 3 dots at the top right, goto "more tools", choose "network conditions", turn of the use of the default user agent and then set Opera to identify as Chrome or Firefox. Then, ctrl + r to reload the page again to test if that helps.
You can also test with Opera's VPN on to test if that makes a difference.