Snap refresh timer stuck

While investigating another issue, I noticed my snap refresh timer was showing the next refresh as 'yesterday'. The snap changes command also did not list any recent changes.

jamesps@ubu20-n-0649f43030:~$ snap refresh --time
timer: 00:00~24:00/4
last: yesterday at 12:05 GMT
next: yesterday at 18:59 GMT

jamesps@ubu20-n-0649f43030:~$ snap changes
no changes found

jamesps@ubu20-n-0649f43030:~$ uptime
 09:41:25 up 8 days, 1:11, 1 user, load average: 1.44, 1.26, 1.20

Checking the snapd.service status showed no issues that I could see.
After manually restarting snapd, the refresh timer was fixed and began a refresh immediately, which then updated VS Code. So a reboot would certainly have fixed the issues. However, I have encountered this problem before and would be useful to know whether snap if failing to refresh or how it even got in this state.

jamesps@ubu20-n-0649f43030:~$ systemctl restart snapd

jamesps@ubu20-n-0649f43030:~$ snap refresh --time
timer: 00:00~24:00/4
last: today at 09:42 GMT
next: n/a

jamesps@ubu20-n-0649f43030:~$ snap changes
ID Status Spawn Ready Summary
13 Done today at 09:42 GMT today at 09:42 GMT Auto-refresh snap "code"

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: snapd 2.54.3+20.04.1ubuntu0.2
ProcVersionSignature: Ubuntu 5.14.0-1024.26-oem 5.14.21
Uname: Linux 5.14.0-1024-oem x86_64
ApportVersion: 2.20.11-0ubuntu27.21
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Fri Mar 4 09:42:57 2022
InstallationDate: Installed on 2021-09-02 (182 days ago)
InstallationMedia: Ubuntu-Server 20.04.2 LTS "Focal Fossa" - Release amd64 (20210201.2)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
 SHELL=/usr/local/bin/bash
SourcePackage: snapd
UpgradeStatus: No upgrade log present (probably fresh install)