This is the originally suspected and still present issue from bug 979042, users complain that package download takes long time. While the original bug fixed the underlying issue there still appears to be a little pause before each download starts. The observed delay is due to how the progress bar is implemented: it is waiting for librepo to tell us the total package size, which for some involved reasons can not do so right away, even though the download has already started. 

As zpavlas pointed out we should be able to deduce this information from the available metadata instead, assigning to Zdenek.