Claude only starts the session timer for your next allowance when you send your first message after a period of no use.

It would be better for you if they started a new one when your current one expired so that there's less time until you get your new allowance when you happen to start using it.

They might do this for UX reasons (the auto-restart looks weird), or they could be trying to get people to upgrade. Maybe both.

A solution I've found is to just say "yo" to Claude every 5 hours. This somewhat decreases the chance that a deep Claude session gets blocked.

yo-claude is an easy way to enable this. Feedback and bug reports welcome.