Steps to replicate issue

1.  Create a group owner workflow, which is grouped on Group as shown below:

2. For decision node, click on Conditions and select the condition where owner is not null.

3. For approval node, select the group owner(id) under Resource.

4. Associate the approval workflow in the main processing workflow.

 

5. Create a request to add groups to a user. A few of the groups should have an owner and some should not.  In the example below, we are requesting three groups:

• The temporary group does not have a group owner.
• AdminGuest has Arun Oberoi as the group owner.
• Administrator has Aaron Beaudoin as the group owner.

6. There are two activities generated for group owner approval:

7. Click on the activity assigned to Aaron Beaudoin.  Despite him being an owner of just the Administrator group, he can see items for a group where he is not the owner: