Output cache not deleting expired caches

I've got an issue in that expired page caches are not being deleted. This is currently happening under v3.1.9 but I've also noticed on some of my old v3 applications it's doing it as well.

On https://www.codeigniter.com/user_guide/g...ching.html, it states that expired caches should be deleted before being refreshed.

If it has expired, it will be deleted and refreshed before being sent to the browser.

Is there something special I should be doing?

I've also noted it talks about having to manually delete cache files if configuration options are changed.

If you change configuration options that might affect your output, you have to manually delete your cache files.

Is there a more in-depth explanation of what configuration options could be changed that would require manual deletion?