When attempting to download any of the provided samples, the progress bar stays empty throughout the process, even though the actual sample file is downloading. I've tested this with Affinity Designer 1.7.1 running on both a 15-inch 2014 MacBook Pro (screenshot attached, shows several minutes in to the download process) and a 13-inch 2016 MacBook Pro, both versions failing to show any progress.
When attempting this on a Windows machine, the progress bar filled up as expected.