What to do about Facebook group members who block admins
Group members will block you and other admins/mods. Don’t tolerate it. Make sure it is clear in your group rules that people who block the admin or the sponsoring Facebook page will be removed (then, remove them right away.)
How to see blocked members:
Facebook lets you see unavailable members. Unfortunately, currently there is no way to decipher between a member who has blocked you and a member who has simply deactivated their Facebook account.
In your group, click on members:
Scroll down to see unavailable members. Click on the kebab menu to the right of each member and select “Remove Member.”