If you are working with guests in Asana, you might not have realized this: if you add two guests as task collaborators, they actually don’t see each other! They only see « Private user ». That makes the collaboration a little bit harder!
If you are curious, I ran a complete study on the topic Who sees whom, a guide to guest visibility with Batman & Robin
Two workarounds are available: give those guests a real account by creating a company email address (you’ll pay for them) or add them at the project or team level (careful about data leak!).
Any other workaround?