PMPro sets up a “cron job” to run every day around midnight that expires the memberships. So it’s possible that a user’s membership set to expire on 2018-06-07 may not be expired until the following day.
Also, if there is something wrong with your cron jobs (low traffic to your site, or heavy caching, lots of things to run during the cron, lots of memberships to expire… all of these can cause timeouts and issues) than your members may not be expired automatically.
Following the directions on this post will sometimes help: https://tommcfarlin.com/wordpress-cron-jobs/
If you are having a more specific issue (maybe it’s only WooCommerce-related memberships that aren’t expiring – although if it sets the expiration date for a user, it should expire them) then provide a bit more detail so we can try to help with that.
Another thing that *sometimes* helps in these cases is to deactivate and reactivate the PMPro plugin to force that cron job to be created again. There are some plugins like WP Crontrol to get more info on the cron jobs setup on your site and how they are running. https://www.ads-software.com/plugins/wp-crontrol/
Let us know if this helps.
