Slow 'core' snap auto-upgrade breaks other snap depending on it

[Enzo Aguado]

The 'core' snap was automatically upgraded on a slow machine overnight. This upgrade took around 5 minutes but during this time, another snap daemon that depended on it restarted and failed with the following error message:

2021-10-07T00:03:19Z [redacted snap name].daemon[276109]: cannot locate base snap core: No such file or directory

Below is the output of 'snap changes' (omitting unrelated changes)

ubuntu@juju-01b2b4-1:~$ snap changes
ID Status Spawn Ready Summary
34 Done yesterday at 06:34 UTC yesterday at 06:34 UTC Change configuration of "core" snap
35 Done yesterday at 07:50 UTC yesterday at 07:50 UTC Change configuration of "core" snap
...
40 Done today at 00:01 UTC today at 00:05 UTC Auto-refresh snaps "core", "lxd", "snapd"

The auto upgrade started at 00:01, my snap restarted at 00:03, and the update was finished at 00:05.
Manually restarting my snap a few hours later worked as expected.

System information:

lsb_release -rd
Description: Ubuntu 20.04.3 LTS
Release: 20.04

ubuntu@juju-01b2b4-1:~$ snap --version
snap 2.51.7
snapd 2.51.7
series 16
ubuntu 20.04
kernel 5.4.0-88-generic

ubuntu@juju-01b2b4-1:~$ snap list
Name Version Rev Tracking Publisher Notes
core 16-2.51.7 11743 latest/stable canonical✓ core
core18 20210722 2128 latest/stable canonical✓ base
core20 20210702 1081 latest/stable canonical✓ base
snapd 2.51.7 13170 latest/stable canonical✓ snapd
(unrelated snaps are omitted)