Ubuntu – How to redirect the output of `apt-file update` into a file

I have a zsh function which updates my system (.deb packages, pip packages, texlive packages, …).

It looks like this:

up() {
  emulate -LR zsh
  [[ -d "${HOME}/log" ]] || mkdir "${HOME}/log"
  LOGFILE="${HOME}/log/update_system.log"
  __update_system 2>&1 | tee -a "${LOGFILE}"
}

The last line calls the __update_system function and pipes its output to tee, which in turn should display the output on the terminal, and append it to a file, so that I can review it later if something went wrong.

One of the commands executed by __update_system is:

$ apt-file update

It seems to be executed, but its output is not logged in the file.
All the other commands (including aptitude update) are logged.

I tried to understand by executing this command in a shell:

$ apt-file update >/tmp/log

Again, apt-file update seems to be executed, but the output is not logged as /tmp/log is empty.

I thought that maybe the output is sent on the standard error, so I tried:

$ apt-file update >/tmp/log 2>&1

But I got the same result, an empty file.

I tried in bash, which also gave me an empty file.

Here are some details about my system:

$ uname -a
Linux ubuntu 4.4.0-135-generic #161-Ubuntu SMP Mon Aug 27 10:45:01 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

About zsh:

$ zsh --version
zsh 5.5.1-dev-0 (x86_64-pc-linux-gnu)

About bash:

$ bash --version
GNU bash, version 4.4.0(1)-release (x86_64-unknown-linux-gnu)

About apt-file:

$ aptitude show apt-file
Package: apt-file
State: installed
Automatically installed: no
Version: 2.5.5ubuntu1
Priority: optional
Section: universe/admin
Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
Architecture: all
Uncompressed Size: 92,2 k
Depends: perl, curl, libconfig-file-perl, libapt-pkg-perl, liblist-moreutils-perl, libregexp-assemble-perl,
         libfile-temp-perl
Suggests: openssh-client, sudo
Description: search for files within Debian packages (command-line interface)
 apt-file is a command line tool for searching files contained in packages for the APT packaging system. You can search
 in which package a file is included or list the contents of a package without installing or fetching it.

How to redirect the output of apt-file update into a file?