The problems are real and actually two. Maybe related to each other.
1. The cached files are NEVER more than 2-3 mb (or maybe slighly more) because a massive clean up (invalidation) happens when a new post is made. So depending on how often we post, the files are cleaned up. That is why they never grow to a big number. Apparently this is a bug, since in 2.9 such a problem doesn’t exist.
2. The second problem is that some times, while a cached file IS created, it is NOT displayed to the user (there is NO stamp) at the end of the page (the page is not served from the cache but as it originally is).