Hi, Matt.
The og:description is usually added through another plugin, probably an SEO plugin. We don’t filter it, but if you let us know which SEO plugin/etc you have that is adding that, we can find the filter to protect that content.
Note that editing the og:description will have SEO impacts on your site. On our sites, only the excerpt or specific description we entered for SEO are shown in the og:description. We are safe to keep sensitive information out of this area. So a work around would just be to edit your excerpts and SEO descriptions.
Another option that might be interesting to you is to have users redirected away from member content instead of relying on PMPro to filter it. We don’t always know how themes and plugins are showing content. Here is a code gist that does that: https://gist.github.com/kimcoleman/be5429f52732dc0d56380cdd4da41636#file-my_template_redirect_require_membership_access-php
There is a bit of a tutorial for our paid membership on that gist: https://www.paidmembershipspro.com/redirect-non-members-away-from-member-content/