I'm not sure if this is a bug or something intentional, but had the following large pop-up during a test. I ran a combined linear test, which completed successfully. I enabled multithread, clicked "Re-test", closed the full screen pop-up ad and the after the first stage of the upload test appeared, it displayed the following large count down and asked me if I want to continue with the test, which then completed successfully
Edit: I ran a handful of further tests, including simultaneously on my mobile (different 4G connection), but didn't get this again.