Likely this, especially if user does not go into the UI very often. Automations not working so go to check it out, hmmm hub has an update every time this happens. If you only check every 30 days there is a high chance there WILL be an update waiting for you, especially with 2.3.9 and now 2.4.0 because they were already working on 2.4.0 while still patching 2.3.9 so there was not much time between the final 2.3.9 and the 2.4.0 release.
Then if you do update at that point, it reboots the hub, which probably fixes the issue. The reboot is what is fixing it, not updating.
Another key point, all your automations run locally. There is nothing that HE can update on thier (optional) cloud services which would cause automations to stop working. You could literality set the hub all up how you want and then totally block it from the internet. It would keep working indefinitely (with occasional reboots I'm sure), without ever going online or updating it again.
