While trying to download Ubuntu, the first download succeeded, but the second download took a very long time to start (on the order of minutes).

WHile waiting for it to start, I tried to start a different download (much smaller) from a different tab, and it took a long time for the download location dialog to come up (the flag was enabled).

URL used for the download:

https://www.ubuntu.com/download/desktop/thank-you?country=US&version=18.04&architecture=amd64

I clicked the "download now" link in the sentence:
"Your download should start automatically. If it doesn’t, download now."