I had the same issue as you. For me it was due to enabling ipv6 and my whonix update-proxy not working with that.
If you enabled ipv6 try disabling it in the sys-net qube as described here (qvm-features ipv4-only-qube ipv6) or disabling it alltogether as described here (qvm-features --unset sys-net ipv6). I only tried the latter and it worked for me!