If I am not logged on to TestMy, and switch to Mulltithread mode, the [Linear] button at the top right does not work. Neither does the 'Disable Multithreading' button.
Steps to reproduce:
Log out of TestMy (or open an incognito/private browser).
Click Multithread at the top-right.
Click the 'Enable Multithreading' button.
Click [Linear] at the top-right.
Click the 'Disable Multithreading' button.
It will continue to display "MultiI Select" at the top-right, sometimes even with the British flag:
I'm not sure if it's related, but if I perform the above steps and then go to the Download page and click the 'Express Test!' button, it display a "Not Found" error page:
I checked this with Chrome, Edge and Firefox.