Qubes Update Tool fails

[apparatus]

What’s your update proxy qube?
Do you have VPN in it?
Maybe your update proxy qube is using IPv6?
There was something similar:

Can't get TemplateVM Update Proxy to work with Firewall or VPN NetVMs

Problem summary: Setting dom0’s /etc/qubes-rpc/policy/qubes.UpdatesProxy AND /etc/qubes/policy.d/30-user.policy TemplateVM target to any NetVM other than a sys-wifi, sys-wired, sys-net, or sys-whonix results in one of two errors: “Reading from proxy failed - read (11: Resource temporarily unavailable) [IP: 127.0.0.1 8082]” OR “Reading from proxy failed - select (115: Operation now in progress) [IP: 127.0.0.1 8082]” (when the qubes-updates-proxy service has been added to the VPN or Firewall NetVM…