I need to find contacts that have been removed from a specific group to add them back again in. I can find using custom search if they're not in a group, but not if they were in a specific group.
Is there a way to find them?
I authored Subscription History Report and it's a good choice, but these days I would use Search Kit (an extension which ships with CiviCRM - Administer menu » System Settings » Extensions.
From there, you can use this (change the domain name):
https://example.org/civicrm/admin/search#/create/Contact?params=%7B%22version%22:4,%22select%22:%5B%22id%22,%22display_name%22,%22Contact_GroupContact_Group_01.title%22%5D,%22orderBy%22:%7B%7D,%22where%22:%5B%5B%22Contact_GroupContact_Group_01.title%22,%22%3D%22,%22Newsletter%20Subscribers%22%5D%5D,%22groupBy%22:%5B%5D,%22join%22:%5B%5B%22Group%20AS%20Contact_GroupContact_Group_01%22,%22INNER%22,%22GroupContact%22,%5B%22id%22,%22%3D%22,%22Contact_GroupContact_Group_01.contact_id%22%5D,%5B%22Contact_GroupContact_Group_01.status:name%22,%22%3D%22,%22%5C%22Removed%5C%22%22%5D%5D%5D,%22having%22:%5B%5D%7D
If you'd prefer to do it yourself, here's a screenshot of the same search:
How about using Subscription History Report