watchtower: watchtower interferes with itself when upgrading itself (regression)

Describe the bug I have a Compose deployment with each container labelled with a watchtower scope, so the watchtower instance started is only responsible for the containers in this stack. Today at 16:35 Eastern (2021-03-28 20:35 UTC), a new latest was pushed to Docker Hub, and the error in #747 reoccurred. This is a regression as previous watchtower self-updates since have succeeded.

To Reproduce Simplified version of the actual compose file used is in the previous issue.

Expected behavior I expected watchtower to update itself as it does with other containers, without sending a bunch of errors, fighting itself, and segfaulting. I also expected the updated container to have the same name as initialized by Compose (emcee-tournament-bot_watchtower_1).

Screenshots

Several containers were created and stuck in the restarting state before I ran docker-compose stop watchtower to stop them all.

$ docker-compose ps
              Name                            Command                  State                Ports
-----------------------------------------------------------------------------------------------------------
MPSyhOBpiqbaarPyXwdTttkdnUkaxzFO   /watchtower                      Exit 1
VtjBBvihCpkMdSpsiasICfdKgBmVaxFj   /watchtower                      Exit 1
dOdfFsesaEctJLoIjbxEHiTdJTBemCUu   /watchtower                      Exit 1
dQSbCsgHvNfKmYmDLzsOkRfLdgaxEqzh   /watchtower                      Exit 1
emcee_adminer_1                    entrypoint.sh docker-php-e ...   Up (healthy)   127.0.0.1:8080->8080/tcp
emcee_backup_1                     /bin/sh -c exec /usr/local ...   Up (healthy)   5432/tcp
emcee_bot_1                        docker-entrypoint.sh node  ...   Up
emcee_postgres_1                   docker-entrypoint.sh postgres    Up (healthy)   127.0.0.1:5432->5432/tcp
emcee_watchtower_1                 /watchtower                      Exit 1
giYjGXQGWNjUeJSsvHkkEltvZsnGnhmX   /watchtower                      Exit 1
mElssuEBGeJMvClfAaiEUTiOuzgRMcjN   /watchtower                      Exit 1
pWEZJHRXUzuEeIJkvXeMbgqYJQhebdun   /watchtower                      Exit 1
qEvzDrawKPMoLHgYTzmYqJRZfoeiOWKH   /watchtower                      Exit 1
ukiTgKPOhnNdQFkvdkoIHizvrkkAneVp   /watchtower                      Exit 1

Environment Ubuntu 18.04.5 LTS, x86_64 Docker version 20.10.2, build 2291f61 docker-compose version 1.27.4, build 40524192

This happened in production so I’m not running with --debug. The logs match the webhook output to Discord.

Additional context Add any other context about the problem here.