We are seeing this issue for this related list called "Contact Relationship"
The message says Unfortunately the related list you're trying to view isn't in the layout, but the related list is really added in the layout. I have checked it several times looking at the page layout assignments of the users.
The users can see the records, but the message shows up when they hover over the record, like in this screenshot:
This related list is being shown inside a Flexi Page, using the Related Lists component (the one that shows all related lists in the layout, not only one).
The name API name of this object is "HealthCloudGA__ContactContactRelation__c".
If anyone knows something it would be greatly appreciated. Thanks!