Dismiss my previous response, your solution is working fine, thanks so much!

Great! But now I have another issue and it makes a lot of sense. In the "No records" transition there's no data so the union (based on "all shared columns") it's not possible as the "No records" transition has 0 records (so it has no columns)   

Hi! I'm using an Union activity after Email delivery to join all profiles who received an email, continuing with an update activity to update a resource.   The issue here is that, if Union activity doesn't receive records from all inbound transitions it won't execute (it's like it keeps waiting for ...

Hi! Did you have an answer? I have the same issue