How to Create a (Block) View of Related Group Content (Nodes)

Create a new content view with at least one block.

Under the view's relationships:

• Select "Content: Parent group"
• Check the "Require this relationship" box

Under contextual arguments:

• Select contextual filter "Group NID" from the dropdown
• Check the "Provide default value" box
• Select "Raw value from URL" from the dropdown and select Path component 2

Under Format, for each and every field, rendered entity or content (depending on which you've selected):

• Select (specify) the "Node group" relationship

Now go to /admin/structure/block, and choose a region of the page you want the block to show up in on the respective node page.

Related issue: #2689663: How to Create View of Related Group Content