I came across this in an environment where the proxy was very slow. The downloaded image for the appliance gets deleted every so often (and perhaps also via the cleanup script), so when it needs to be reloaded from the internet, it can take its time, because its quite large (>1GB).

Another source of trouble can be that PackageKit or simply another instance of yum/dnf is already running and that is blocking the download. Check with htop or similar.https://lists.ovirt.org/archives/list/users@ovirt.org/message/HDY6W2N2VJURBPP35YWDDRPCL6F2HUY4/