Using the Group module β in site build along with this module. All nodes have the entity reference field: "Collaborators". This field allows authors to grant editing permissions via the Access by Reference module.
Nodes can also be created in a Group.
However, when a node is created in a group, the permission set by the AbR module are ignored and the referenced users do not have edit permissions.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.