I encountered the very same thing with an otherwise perfectly functional Whonix 8 Workstation. That is to say: 3 attempts to install it, 2 of them failed after 4-5 hours each, last one succeeded (also after 4-5 hours). Pretty long for 23 MB of download. It works but it is a game of chance.
During my last attempt, I started the updater from the commandline and noticed that it’s downloading from some Torproject onion address - maybe this is the reason, don’t know!