I don't know if anyone looks at apt-cacher-ng bug reports, but reassigning it there for further analysis.
The log says that this is apt-cacher-ng failing to talk to launchpad.
I generally recommend avoiding apt-cacher-ng due to bugs in the interaction with apt (which then go in endless circles of blame between both sides, but not resolved) and using squid instead if a proxy is needed.
I don't know if anyone looks at apt-cacher-ng bug reports, but reassigning it there for further analysis.
The log says that this is apt-cacher-ng failing to talk to launchpad.
I generally recommend avoiding apt-cacher-ng due to bugs in the interaction with apt (which then go in endless circles of blame between both sides, but not resolved) and using squid instead if a proxy is needed.