<p>From 31 October 2024, BT Cloud has <a href="https://www.bt.com/help/broadband/bt-cloud/getting-set-up/download-or-access-files/how-do-i-download-files--folders-and-devices-from-bt-cloud-">closed</a> and all data will soon be deleted.</p>
All the latest versions of chrome and Firefox use the system default values for multi-threading downloads, so looks like you've got it disabled on your Windows setup by default. It's easy enough to override in the browser settings.
Seem similar issues reported before over Openreach FTTP on various ISPs. Poor single thread performance but good enough multi thread. Engineer checks always come back ok.
