acng maintainence fails because ports.ubuntu.com does not have any i386 files

I have machines using a normal mirror (gb.archive‥), and I have machines using the ports mirror (because the packages are not available on the main mirror: arm64, for example).

For reasons I simply do not understand, acng attempts to look for i386 files on ports.ubuntu.com.

I have never asked an i386 machine to contact ports.ubuntu.com so I do not know why acng is trying to do so. I also do not have ports.ubuntu.com listed as a mirror.

Why is it doing this?

The result being that the cron job fails every time, and sends me an annoying e-mail.

/etc/cron.daily/apt-cacher-ng:
Maintenance Task: Expiration
See file /var/log/apt-cacher-ng/maint_1532282661.log.html for more details.
Server url: http://localhost:3142//acng-report.html?doExpire=Start+Expiration&abortOnErrors=aOe
Problem with ports.ubuntu.com/dists/bionic/restricted/binary-i386/Packages.xz
Problem with ports.ubuntu.com/dists/bionic/multiverse/binary-i386/Packages.xz
Problem with ports.ubuntu.com/dists/bionic/main/binary-i386/Packages.xz
Problem with ports.ubuntu.com/dists/bionic/universe/binary-i386/Packages.xz

I've tried dumping my cache but this eventually reappears.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: apt-cacher-ng 0.9.1-1ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-24.26~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-24-generic i686
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: i386
CurrentDesktop: MATE
Date: Sun Jul 22 22:46:28 2018
SourcePackage: apt-cacher-ng
UpgradeStatus: Upgraded to xenial on 2017-11-14 (250 days ago)
modified.conffile..etc.apt-cacher-ng.security.conf: [inaccessible: [Errno 13] Permission denied: '/etc/apt-cacher-ng/security.conf']
mtime.conffile..etc.apt-cacher-ng.acng.conf: 2017-11-10T21:56:55
mtime.conffile..etc.logrotate.d.apt-cacher-ng: 2018-06-13T07:51:26